Exposure apparatus, exposure method, and device manufacturing method

ABSTRACT

An exposure apparatus is equipped with an encoder system which measures positional information of a wafer stage by irradiating a measurement beam using four heads installed on the wafer stage on a scale plate which covers the movement range of the wafer stage except for the area right under a projection optical system. Placement distances of the heads here are each set to be larger than width of the opening of the scale plates, respectively. This allows the positional information of the wafer stage to be measured, by switching and using the three heads facing the scale plate out of the four heads according to the position of the wafer stage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 14/970,116, filed Dec. 15,2015, which is a division of application Ser. No. 14/661,903, filed Mar.18, 2015, now U.S. Pat. No. 9,244,367, which is a division ofapplication Ser. No. 13/921,502, filed Jun. 19, 2013, now U.S. Pat. No.9,019,472, which is a division of application Ser. No. 12/859,983 filedAug. 20, 2010, now U.S. Pat. No. 8,493,547, which in turn is anon-provisional application, which claims the benefit of U.S.Provisional Application No. 61/236,701 filed Aug. 25, 2009. Thedisclosure of the prior applications is hereby incorporated by referenceherein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to exposure apparatuses, exposure methods,and device manufacturing methods, and more particularly to an exposureapparatus and an exposure method used in a lithography process tomanufacture microdevices such as a semiconductor device, and a devicemanufacturing method using the exposure method.

2. Description of the Background Art

Conventionally, in a lithography process for manufacturing electrondevices (microdevices) such as semiconductor devices (such as integratedcircuits) and liquid crystal display devices, exposure apparatuses suchas a projection exposure apparatus by a step-and-repeat method (aso-called stepper), or a projection exposure apparatus by astep-and-scan method (a so-called scanning stepper (which is also calleda scanner) is mainly used.

In these types of exposure apparatuses, with finer device patterns dueto higher integration of semiconductor devices, requirements for highoverlay accuracy (alignment accuracy) is increasing. Therefore,requirements for higher accuracy is increasing, also in positionmeasurement of substrates such as a wafer or a glass plate and the likeon which a pattern is formed.

As an apparatus to meet such requirements, for example, in U.S. PatentApplication Publication No. 2006/0227309, an exposure apparatus isproposed which is equipped with a position measurement system using aplurality of encoder type sensors (encoder heads) installed on asubstrate table. In this exposure apparatus, the encoder head irradiatesa measurement beam on a scale which is placed facing a substrate table,and measures the position of the substrate table by receiving a returnbeam from the scale.

However, in the exposure apparatus which is equipped with the positionmeasurement system described in U.S. Patent Application Publication No.2006/0227309, as for the actual operation, the encoder head facing thescale has to be switched from a plurality of encoder heads according tothe position of the substrate table. Furthermore, when switching theencoder head which is to be used, continuity of the position measurementresults of the substrate table also has to be secured.

SUMMARY OF THE INVENTION

The present invention was made under the circumstances described above,and according to a first aspect, there is provided a first exposureapparatus which sequentially exposes an energy beam on a plurality ofdivided areas placed in a shape of a matrix on an object, and forms apattern on each of the plurality of divided areas, the apparatuscomprising: a movable body which holds the object and moves along apredetermined plane; a position measurement system which has a pluralityof heads provided on the movable body, and of the plurality of heads,obtains a positional information of the movable body, based onmeasurement results of a predetermined number of heads which irradiate ameasurement beam on a measurement plane that has an opening partiallyand is placed facing the movable body and roughly parallel to thepredetermined plane, receive a return beam from the measurement plane,and measure a position of the movable body in each measurementdirection; and a control system which drives the movable body based onthe positional information obtained by the position measurement system,and also switches at least one of the predetermined number of heads usedto compute a positional information of the movable body according to aposition of the movable body to a different head, wherein of theplurality of heads, a separation distance of two heads set apart in afirst direction within the predetermined plane is larger than a width ofthe opening in the first direction.

According to this apparatus, it becomes possible to measure thepositional information of a movable body by switching and using encoderheads facing a scale from a plurality of encoder heads according to theposition of the movable body.

According to a second aspect of the present invention, there is provideda second exposure apparatus which sequentially exposes an energy beam ona plurality of divided areas on an object, and forms a pattern on eachof the plurality of divided areas on the object, the apparatuscomprising: a movable body which holds the object and moves along apredetermined plane; a position measurement system which has a pluralityof heads provided on the movable body, and of the plurality of heads,irradiates a measurement beam on a measurement plane having ameasurement non-effective area in part of the measurement plane which isplaced facing the movable body and roughly parallel to the predeterminedplane, receives a return beam from the measurement plane, and obtains apositional information of the movable body based on measurement resultsof a predetermined number of heads which measure a position of themovable body in each measurement direction; and a control system whichdrives the movable body based on the positional information obtained bythe position measurement system, while switching a head to be used tocompute the positional information of the movable body, wherein of theplurality of heads, a separation distance of two heads set apart in apredetermined direction within the predetermined plane is decided,taking into consideration a size of the measurement non-effective areain the predetermined direction.

According to this apparatus, because the separation distance between thetwo heads is decided adequately taking into consideration the size of ameasurement non-effective area in a predetermined direction, thepositional information of the movable body can be measured withoutswitching the heads while the movable body performs a constant speedmovement in a predetermined direction to form a pattern on a dividedarea subject to formation on the object. Accordingly, it becomespossible to form a pattern on the object with good precision.

According to a third aspect of the present invention, there is provideda third exposure apparatus which sequentially exposes an energy beam ona plurality of divided areas placed in a shape of a matrix on an object,and forms a pattern on each of the plurality of divided areas, theapparatus comprising: a movable body which holds the object and movesalong a predetermined plane; a position measurement system which has aplurality of heads provided on the movable body, and of the plurality ofheads, irradiates a measurement beam on a measurement plane having anopening in part of the measurement plane which is placed facing themovable body and roughly parallel to the predetermined plane, receives areturn beam from the measurement plane, and obtains a positionalinformation of the movable body based on measurement results of apredetermined number of heads which measure a position of the movablebody in each measurement direction; and a control system which drivesthe movable body based on positional information obtained by theposition measurement system, and also switches at least one of thepredetermined number of heads used to compute a positional informationof the movable body according to a position of the movable body to adifferent head, wherein after a constant speed movement on the movablebody is performed in a first area where heads included in a first headgroup and a second head group which has at least one different head ofthe plurality of heads face the measurement plane, in a first directionof the predetermined plane to form the pattern in a divided area subjectto formation of the plurality of divided areas based on the positionalinformation of the movable body which is obtained based on measurementresults of the first head group, heads used to compute positionalinformation of the movable body are switched to the second head groupbefore the movable body moves from the first area to a second area whereonly the heads included in the second head group face the measurementplane.

According to this apparatus, the positional information of the movablebody can be measured without switching the heads while the movable bodyperforms a constant speed movement in the first direction to form apattern on a divided area subject to formation on the object.Accordingly, it becomes possible to form a pattern on the object withgood precision.

According to a fourth aspect of the present invention, there is provideda first exposure method in which a plurality of divided areas placed ina shape of a matrix on an object is sequentially exposed an energy beam,and a pattern is formed on each of the plurality of divided areas, themethod comprising: obtaining a positional information of the movablebody, based on measurement results of a predetermined number of heads ofthe plurality of heads provided on the movable body which moves along apredetermined plane holding the object, by irradiating a measurementbeam on a measurement plane having an opening in part of the measurementplane which is placed facing the movable body and roughly parallel tothe predetermined plane, receiving a return beam from the measurementplane, and measuring a position of the movable body in each measurementdirection; moving the movable body at a constant speed in the firstdirection in the predetermined plane to form the pattern in a dividedarea subject to formation of the plurality of divided areas, based onthe positional information; and after the movable body is moved at aconstant speed, switching at least one of the predetermined number ofheads used to compute a positional information of the movable bodyaccording to a position of the movable body to a different head.

According to this method, the positional information of the movable bodycan be measured without switching the heads while the movable bodyperforms a constant speed movement in the first direction to form apattern on a divided area subject to formation on the object.Accordingly, it becomes possible to form a pattern on the object withgood precision.

According to a fifth aspect of the present invention, there is provideda second exposure method in which a plurality of divided areas placed ina shape of a matrix on an object is sequentially exposed by an energybeam, and a pattern is formed on each of the plurality of divided areas,the method comprising: obtaining a positional information of the movablebody, based on measurement results of a predetermined number of heads ofthe plurality of heads provided on the movable body which moves along apredetermined plane holding the object, by irradiating a measurementbeam on a measurement plane having an opening in part of the measurementplane which is placed facing the movable body and roughly parallel tothe predetermined plane, receiving a return beam from the measurementplane, and measuring a position of the movable body in each measurementdirection; stepping and driving the movable body toward a starting pointof a constant speed drive to form the pattern in a divided area subjectto formation of the plurality of divided areas, based on the positionalinformation obtained; and switching at least one of the predeterminednumber of heads used to compute a positional information of the movablebody according to a position of the movable body to a different headbefore the movable body is moved at a constant speed in the firstdirection to form the pattern in the divided area subject to formation,after the stepping and driving.

According to this method, the positional information of the movable bodycan be measured without switching the heads while the movable bodyperforms a constant speed movement in the first direction to form apattern on a divided area subject to formation on the object.

According to a sixth aspect of the present invention, there is provideda third exposure method in which a plurality of divided areas placed ina shape of a matrix on an object is sequentially exposed by an energybeam, and a pattern is formed on each of the plurality of divided areas,the method comprising: obtaining positional information of the movablebody within a first area where of a plurality of heads provided on amovable body which moves along a predetermined plane holding the object,heads included in a first head group and a second head group which hasat least one head different from the first head group face a measurementplane which is provided roughly parallel to the predetermined plane,based on measurement results of the first head group, and performing aconstant speed drive of the movable body in a first direction of thepredetermined plane to form the pattern on a divided area subject toformation of the plurality of divided areas, based on the positionalinformation; and switching heads to be used to compute the positionalinformation to the second heads group after the constant speed movement,before the movable body moves from the first area to a second area whereheads included only in the second group face the measurement plane.

According to this method, the positional information of the movable bodycan be measured without switching the heads while the movable bodyperforms a constant speed movement in the first direction to form apattern on a divided area subject to formation on the object.Accordingly, it becomes possible to form a pattern on the object withgood precision.

According to a seventh aspect of the present invention, there isprovided a fourth exposure method in which a plurality of divided areasplaced in a shape of a matrix on an object is sequentially exposed by anenergy beam, and a pattern is formed on each of the plurality of dividedareas, the method comprising: obtaining positional information of themovable body within a first area where of a plurality of heads providedon a movable body which moves along a predetermined plane holding theobject, heads included in a first head group and a second head groupwhich has at least one head different from the first head group face ameasurement plane which is provided roughly parallel to thepredetermined plane, based on measurement results of the first headgroup, and performing a step drive of the movable body toward a startingposition of the constant speed movement to form the pattern on a dividedarea subject to formation of the plurality of divided areas, based onthe positional information; and switching heads to be used to measurethe positional information to the second heads group after the stepdrive, before the movable body moves from the first area to the secondarea by being moved from the starting position in the first direction bythe constant speed movement to form the pattern on a divided areasubject to formation.

According to this method, the positional information of the movable bodycan be measured without switching the heads while the movable bodyperforms a constant speed movement in the first direction to form apattern on a divided area subject to formation on the object.Accordingly, it becomes possible to form a pattern on the object withgood precision.

According to an eighth aspect of the present invention, there isprovided a fourth exposure apparatus which sequentially exposes anenergy beam on a plurality of divided areas placed in a shape of amatrix on an object, and forms a pattern on each of the plurality ofdivided areas, the apparatus comprising: a movable body which holds theobject and moves along a predetermined plane; a position measurementsystem which has a plurality of heads provided on the movable body, andobtains positional information of the movable body based on measurementresults of a predetermined number of heads of the plurality of headswhich is obtained by irradiating a measurement beam on a measurementplane placed roughly parallel to the predetermined plane facing themovable body, receiving a return beam from the measurement plane, andmeasuring a position of the movable body in each measurement direction;and a control system which drives the movable body based on positionalinformation obtained from the position measurement system, as well asswitch at least one head of the predetermined number of heads used tocompute the positional information of the body at the time besides whena constant speed movement of the movable body is performed in a firstdirection within the predetermined plane to form the pattern in thedivided area subject to formation of the plurality of divided areas toanother head.

According to this apparatus, while the movable body performs a constantspeed movement in the first direction to form a pattern on a dividedarea subject to formation on the object, the head is not switched.Accordingly, it becomes possible to form a pattern on the object withgood precision.

According to the ninth embodiment of the present invention, there isprovided a fifth exposure method in which a plurality of divided areasplaced in a shape of a matrix on an object is sequentially exposed by anenergy beam, and a pattern is formed on each of the plurality of dividedareas, the method comprising: obtaining a positional information of themovable body, based on measurement results of a predetermined number ofheads of the plurality of heads provided on the movable body which movesalong a predetermined plane holding the object, by irradiating ameasurement beam on a measurement plane having an opening in part of themeasurement plane which is placed facing the movable body and roughlyparallel to the predetermined plane, receiving a return beam from themeasurement plane, and measuring a position of the movable body in eachmeasurement direction; switching at least one of the predeterminednumber of heads used to compute a positional information of the movablebody according to a position of the movable body to a different head ata time besides when the movable body performs the constant speedmovement in the first direction to form the pattern in the divided areasubject to formation.

According to this method, while the movable body performs a constantspeed movement in the first direction to form a pattern on a dividedarea subject to formation on the object, the head is not switched.Accordingly, it becomes possible to form a pattern on the object withgood precision.

According to a tenth aspect of the present invention, there is provideda device manufacturing method, including forming a pattern on an objectusing any one of the first to fifth exposure methods of the presentinvention; and developing the object on which the pattern is formed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings;

FIG. 1 is a view schematically showing the configuration of an exposureapparatus related to an embodiment;

FIG. 2 is a view showing a configuration of an encoder system placed inthe periphery of a projection optical system;

FIG. 3 is a view showing a configuration of an encoder system placed inthe periphery of an alignment system;

FIG. 4 is an enlarged view of a wafer stage partially fractured;

FIG. 5 is a view showing a placement of encoder heads on the waferstage;

FIG. 6 is a block diagram showing the main configuration of the controlsystem related with the stage control in the exposure apparatus in FIG.1;

FIG. 7 is a view (No. 1) showing a relation between a placement ofencoder heads and a scale plate and a measurement area of the encodersystem;

FIG. 8 is an enlarged view of wafer W1 in FIG. 7;

FIG. 9 is a view (No. 1) showing a movement track of an exposure centeron a wafer in an exposure by a step-and-scan method;

FIG. 10A is a view (No. 1) showing an example of a switching procedureof encoder heads, FIG. 10B is a view showing a temporal change of thedrive speed of the wafer stage before and after the switching, and FIGS.10C and 10D are views (No. 2 and 3) showing an example of a switchingprocedure of encoder heads;

FIGS. 11A and 11B are views used to explain a linkage computing and alinkage process;

FIG. 12 is a view showing a rough configuration of a linkage process atthe time when switching the encoder heads;

FIG. 13 is a view (No. 2) showing a relation between a placement of theencoder heads and the scale plate and the measurement area of theencoder system;

FIG. 14 is an enlarged view of wafer W2 in FIG. 13;

FIG. 15 is a view (No. 2) showing a movement track of the exposurecenter on a wafer in an exposure by a step-and-scan method;

FIGS. 16A to 16C are views (No. 4 to 6) showing an example of aswitching procedure of encoder heads; and

FIGS. 17A and 17B are views used to explain an occurrence principle ofmeasurement errors in the encoder system involved with the accelerationof the wafer stage.

DESCRIPTION OF THE EMBODIMENTS

An embodiment of the present invention will be described below, withreference to FIGS. 1 to 17B.

FIG. 1 schematically shows the configuration of an exposure apparatus100 related to the present embodiment. Exposure apparatus 100 is aprojection exposure apparatus of the step-and-scan method, namely theso-called scanner. As it will be described later, a projection opticalsystem PL is arranged in the embodiment, and in the description below, adirection parallel to an optical axis AX of projection optical system PLwill be described as the Z-axis direction, a direction within a planeorthogonal to the Z-axis direction in which a reticle and a wafer arerelatively scanned will be described as the Y-axis direction, adirection orthogonal to the Z-axis and the Y-axis will be described asthe X-axis direction, and rotational (inclination) directions around theX-axis, the Y-axis, and the Z-axis will be described as θx, θy, and θzdirections, respectively.

Exposure apparatus 100 is equipped with an illumination system 10, areticle stage RST holding reticle R, a projection unit PU, a wafer stagedevice 50 including wafer stages WST1 and WST2 on which a wafer W ismounted, a control system for these parts and the like.

Illumination system 10 includes a light source, an illuminanceuniformity optical system, which includes an optical integrator and thelike, and an illumination optical system that has a reticle blind andthe like (none of which are shown), as is disclosed in, for example,U.S. Patent Application Publication No. 2003/0025890 and the like.Illumination system 10 illuminates a slit-shaped illumination area IAR,which is set on reticle R with a reticle blind (a masking system), by anillumination light (exposure light) IL with a substantially uniformilluminance. Here, as one example, ArF excimer laser light (with awavelength of 193 nm) is used as the illumination light IL.

On reticle stage RST, reticle R on which a circuit pattern or the likeis formed on its pattern surface (the lower surface in FIG. 1) is fixed,for example, by vacuum chucking. Reticle stage RST is finely drivablewithin an XY plane, for example, by a reticle stage drive section 11(not shown in FIG. 1, refer to FIG. 6) that includes a linear motor orthe like, and reticle stage RST is also drivable in a scanning direction(in this case, the Y-axis direction, which is a direction orthogonal tothe page surface in FIG. 1) at a predetermined scanning speed.

The positional information (including position information in the θzdirection (θz rotation quantity)) of reticle stage RST in the XY plane(movement plane) is constantly detected, for example, at a resolution ofaround 0.25 nm by a reticle laser interferometer (hereinafter referredto as a “reticle interferometer”) 16, which irradiates a measurementbeam on a movable mirror 15 (the mirrors actually arranged are a Ymovable mirror (or a retro reflector) that has a reflection surfacewhich is orthogonal to the Y-axis direction and an X movable mirror thathas a reflection surface orthogonal to the X-axis direction) shown inFIG. 1. Incidentally, to measure the positional information of reticle Rat least in directions of three degrees of freedom, instead of, ortogether with reticle interferometer 16, the encoder system which isdisclosed in, for example, U.S. Patent Application Publication No.2007/0288121 and the like can be used.

Projection unit PU is placed below (−Z side) reticle stage RST in FIG.1, and is held by a main frame (not shown) (metrology frame) whichconfigures a part of a body. Projection unit PU has a barrel 40, and aprojection optical system PL consisting of a plurality of opticalelements held by barrel 40. As projection optical system PL, forexample, a dioptric system is used, consisting of a plurality of lenses(lens elements) that has been disposed along optical axis AX, which isparallel to the Z-axis direction. Projection optical system PL is, forexample, a both-side telecentric dioptric system that has apredetermined projection magnification (such as one-quarter, one-fifth,or one-eighth times). Therefore, when illumination light IL fromillumination system 10 illuminates illumination area IAR, illuminationlight IL that has passed through reticle R which is placed so that itspattern surface substantially coincides with a first plane (an objectplane) of projection optical system PL forms a reduced image of thecircuit pattern (a reduced image of a part of the circuit pattern) ofreticle R formed within illumination area IAR, via projection opticalsystem PL, in an area (exposure area) IA conjugate to illumination areaIAR on wafer W whose surface is coated with a resist (a sensitive agent)and is placed on a second plane (an image plane) side of projectionoptical system PL. And by reticle stage RST and wafer stages WST1 andWST2 being synchronously driven, reticle R is relatively moved in thescanning direction (the Y-axis direction) with respect to illuminationarea IAR (illumination light IL) while wafer W is relatively moved inthe scanning direction (the Y-axis direction) with respect to exposurearea IA (illumination light IL), thus scanning exposure of a shot area(divided area) on wafer W is performed, and the pattern of reticle R istransferred onto the shot area. That is, in the embodiment, the patternof reticle R is generated on wafer W according to illumination system 10and projection optical system PL, and then by the exposure of thesensitive layer (resist layer) on wafer W with illumination light IL,the pattern is formed on wafer W.

Incidentally, the main frame can be one of a gate type frame which isconventionally used, and a hanging support type frame disclosed in, forexample, U.S. Patent Application Publication No. 2008/0068568 and thelike.

In the periphery on the −Z side end of barrel 40, for example, a scaleplate 21 is placed parallel to the XY plane, at a height substantiallyflush with a surface on the lower end of barrel 40. As shown in FIG. 2in the embodiment, scale plate 21 is configured of four L-shapedsections (parts) 21 ₁, 21 ₂, 21 ₃, and 21 ₄, and the −Z end of barrel 40is inserted, for example, inside a rectangular shaped opening 21 aformed in the center. In this case, the width in the X-axis directionand the Y-axis direction of scale plate 21 is a and b, respectively, andthe width of opening 21 a in the X-axis direction and the Y-axisdirection is a_(i) and b_(i), respectively.

At a position away from scale plate 21 in the +X direction is a scaleplate 22, which is placed substantially flush with scale plate 21, asshown in FIG. 1. Scale plate 22 is also configured, for example, of fourL-shaped sections (parts) 22 ₁, 22 ₂, 22 ₃, and 22 ₄ as is shown in FIG.3, and the −Z end of an alignment system ALG which will be describedlater is inserted, for example, inside a rectangular shaped opening 22 aformed in the center. The width in the X-axis direction and the Y-axisdirection of scale plate 22 is a and b, respectively, and the width ofopening 22 a in the X-axis direction and the Y-axis direction is a_(i)and b_(i), respectively. Incidentally, in the embodiment, while thewidth of scale plates 21 and 22, and the width of openings 21 a and 22 ain the X-axis and the Y-axis directions were the same, the width doesnot necessarily have to be the same, and the width may differ in atleast one of the X-axis and the Y-axis directions.

In the embodiment, scale plates 21 and 22 are supported by suspensionfrom a main frame (not shown) (metrology frame) which supportsprojection unit PU and alignment system ALG. On the lower surface (asurface on the −Z side) of scale plates 21 and 22, a reflection typetwo-dimensional diffraction grating RG (refer to FIGS. 2, 3, and 4) isformed, consisting of a grating of a predetermined pitch, such as, forexample, a grating of 1 μm whose periodic direction is in a direction of45 degrees with the X-axis serving as a reference (a direction of −45degrees when the Y-axis serves as a reference), and a grating of apredetermined pitch, such as, for example, a grating of 1 μm, whoseperiodic direction is in a direction of −45 degrees with the X-axisserving as a reference (−135 degrees when the Y-axis serves as areference). However, due to the configuration of the two-dimensionalgrating RG and an encoder head which will be described later on, anon-effective area having a width t is included in each of the vicinityof the outer periphery of sections 21 ₁ to 21 ₄ and 22 ₁ to 22 ₄configuring scale plates 21 and 22. The two-dimensional grating RG ofscale plates 21 and 22 covers a movement range of wafer stages WST1 andWST2, respectively, at least at the time of exposure operation andalignment (measurement).

Wafer stage device 50, as shown in FIG. 1, is equipped with a stage base12 supported almost horizontally by a plurality of (for example, threeor four) vibration isolation mechanisms (omitted in the drawings) on thefloor surface, wafer stages WST1 and WST2 placed on stage base 12, awafer stage drive system 27 (only a part of the system shown in FIG. 1,refer to FIG. 6) which drives wafer stages WST1 and WST2, and ameasurement system which measures the position of wafer stages WST1 andWST2 and the like. The measurement system is equipped with encodersystems 70 and 71, and a wafer laser interferometer system (hereinaftersimply referred to as a wafer interferometer system) 18 and the likeshown in FIG. 6. Incidentally, encoder systems 70 and 71, and waferinterferometer system 18 will be further described later in thedescription. However, in the embodiment, wafer interferometer system 18does not necessarily have to be provided.

As shown in FIG. 1, stage base 12 is made of a member having a tabularform, and the degree of flatness of the upper surface is extremely highand serves as a guide surface when wafer stages WST1 and WST2 move.Inside stage base 12, a coil unit is housed, including a plurality ofcoils 14 a placed in the shape of a matrix with the XY two-dimensionaldirection serving as a row direction and a column direction.

Incidentally, another base member to support the base by levitation canbe provided separately from stage base 12, and stage base 12 can be madeto function as a counter mass (reaction force canceller) which movesaccording to the law of conservation of momentum by the reaction forceof the drive force of wafer stages WST1 and WST2.

As shown in FIG. 1, wafer stage WST1 has a stage main section 91, and awafer table WTB1 which is placed above stage main section 91 and issupported in a non-contact manner with respect to stage main section 91by a Z tilt drive mechanism (not shown). In this case, wafer table WTB1is supported in a non-contact manner by Z tilt drive mechanism byadjusting the balance of the upward force (repulsion) such as theelectromagnetic force and the downward force (gravitation) including theself-weight at three points, and is also finely driven at least indirections of three degrees of freedom, which are the Z-axis direction,the θx direction, and the θy direction. At the bottom of stage mainsection 91, a slider section 91 a is arranged. Slider section 91 a has amagnet unit made up of a plurality of magnets arranged two-dimensionallywithin the XY plane, a housing to house the magnetic unit, and aplurality of air bearings arranged in the periphery of the bottomsurface of the housing. The magnet unit configures a planar motor 30which uses the drive of an electromagnetic force (the Lorentz force) asdisclosed in, for example, U.S. Pat. No. 5,196,745, along with the coilunit previously described. Incidentally, as planar motor 30, the drivemethod is not limited the Lorentz force drive method, and a planar motorby a variable reluctance drive system can also be used.

Wafer stage WST1 is supported by levitation above stage base 12 by apredetermined clearance (clearance gap/distance/gap/spatial distance),such as around several μm, by the plurality of air bearings describedabove, and is driven in the X-axis direction, the Y-axis direction, andthe θz direction by planar motor 30. Accordingly, wafer table WTB1(wafer W) is drivable with respect to stage base 12 in directions of sixdegrees of freedom (hereinafter shortly described as the X-axisdirection, the Y-axis direction, the Z-axis direction, the θx direction,the θy direction, and the θz direction (hereinafter X, Y, Z, θx, θy,θz)).

In the embodiment, a main controller 20 controls the magnitude anddirection of current supplied each of the coils 14 a configuring thecoil unit. Wafer stage drive system 27 is configured, including planarmotor 30 and the Z tilt drive mechanism previously described.Incidentally, planar motor 30 is not limited to a motor using a movingmagnet method, and can be a motor using a moving coil method. Further,as planar motor 30, a magnetic levitation type planar motor can be used.In this case, the air bearing previously described does not have to bearranged. Further, wafer stage WST can be driven in directions of sixdegrees of freedom by planar motor 30. Further, wafer table WTB1 can bemade finely movable in at least one of the X-axis direction, the Y-axisdirection, and the θZ direction. More specifically, wafer stage WST1 canbe configured by a rough/fine movement stage.

On wafer table WTB1, wafer W is mounted via a wafer holder (not shown),and is fixed by a chuck mechanism (not shown), such as, for example,vacuum suction (or electrostatic adsorption). Although it is not shown,on one of the diagonal lines on wafer table WTB1, a first fiducial markplate and a second fiducial mark plate are provided, with the waferholder in between. On the upper surface of the first and second fiducialmark plates, a plurality of reference marks which are detected by a pairof reticle alignment systems 13A and 13B and alignment system ALG areformed, respectively. Incidentally, the positional relation between theplurality of reference marks on the first and second fiducial plates areto be known.

Wafer stage WST2 is also configured in a similar manner as wafer stageWST1.

Encoder systems 70 and 71 obtain (measure) positional information ofwafer stages WST1 and WST2, respectively, in directions of six degreesof freedom (X, Y, Z, θx, θy, θz) in an exposure time movement area (inan area where the wafer stage moves when exposing a plurality of shotareas on wafer W) including an area right below projection opticalsystem PL, and in an alignment time movement area including an arearight below alignment system ALG. Now, a configuration and the like ofencoder systems 70 and 71 will be described in detail. Incidentally,exposure time movement area (a first movement area) is an area in whichthe wafer stage moves during an exposure operation within the exposurestation (a first area) where the exposure of the wafer is performed viaprojection optical system PL, and the exposure operation, for example,includes not only exposure of all of the shot areas on the wafer towhich the pattern should be transferred, but also the preparatoryoperations (for example, detection of the fiducial marks previouslydescribed) for exposure. Measurement time movement area (a secondmovement area) is an area in which the wafer stage moves during ameasurement operation within the measurement station (a second area)where the measurement of the positional information is performed bydetection of alignment marks on the wafer by alignment system ALG, andthe measurement operation, for example, includes not only detection of aplurality of alignment marks on the wafer, but also detection(furthermore, measurement of positional information (step information)of the wafer in the Z-axis direction) of fiducial marks by alignmentsystem ALG

In wafer tables WTB1 and WTB2, as shown in an planar view in FIGS. 2 and3, respectively, encoder heads (hereinafter appropriately referred to asa head) 60 ₁ to 60 ₄ are placed in each of the four corners on the uppersurface. In this case, the separation distance in the X-axis directionbetween heads 60 ₁ and 60 ₂ and the separation distance in the X-axisdirection between heads 60 ₃ and 60 ₄ are both equal to A. Further, theseparation distance in the Y-axis direction between heads 60 ₁ and 60 ₄and the separation distance in the Y-axis direction between heads 60 ₂and 60 ₃ are both equal to B. These separation distances A and B arelarger than width a_(i) and b_(i) of opening 21 a of scale plate 21.Specifically, taking into consideration width t of the non-effectivearea previously described, A≧a_(i)+2t, B≧b_(i)+2t. Heads 60 ₁ to 60 ₄are housed, respectively, inside holes of a predetermined depth in theZ-axis direction which have been formed in wafer tables WTB1 and WTB2 asshown in FIG. 4, with head 60 ₁ taken up as a representative.

As shown in FIG. 5, head 60 ₁ is a two-dimensional head in a −135degrees direction with the X-axis serving as a reference (in otherwords, a −45 degrees direction with the X-axis serving as a reference)and whose measurement direction is in the Z-axis direction. Similarly,heads 60 ₂ to 60 ₄ are two-dimensional heads that are in a 225 degreesdirection with the X-axis serving as a reference (in other words, a 45degrees direction with the X-axis serving as a reference) whosemeasurement direction is in the Z-axis direction, a 315 degreesdirection with the X-axis serving as a reference (in other words, a −45degrees direction with the X-axis serving as a reference) whosemeasurement direction is in the Z-axis direction, and a 45 degreesdirection with the X-axis serving as a reference whose measurementdirection is in the Z-axis direction, respectively. As is obvious fromFIGS. 2 and 4, heads 60 ₁ to 60 ₄ irradiate a measurement beam on thetwo dimensional diffraction grating RG formed on the surface of sections21 ₁ to 21 ₄ of scale plate 21 or sections 22 ₁ to 22 ₄ of scale plate22 that face the heads, respectively, and by receiving thereflected/diffraction beams from the two-dimensional grating, measurethe position of wafer table WTB1 and WTB2 (wafer stages WST1 and WST2)for each of the measurement directions. Now, as each of the heads 60 ₁to 60 ₄, a sensor head having a configuration similar to a sensor headfor measuring variation as is disclosed in, for example, U.S. Pat. No.7,561,280, can be used.

In heads 60 ₁ to 60 ₄ configured in the manner described above, sincethe optical path lengths of the measurement beams in air are extremelyshort, the influence of air fluctuation can mostly be ignored. However,in the embodiment, the light source and a photodetector are arrangedexternal to each head, or more specifically, inside (or outside) stagemain section 91, and only the optical system is arranged inside of eachhead. And the light source, the photodetector, and the optical systemare optically connected via an optical fiber (not shown). In order toimprove the positioning precision of wafer table WTB (fine movementstage), air transmission of a laser beam and the like can be performedbetween stage main section 91 (rough movement stage) and wafer table WTB(fine movement stage) (hereinafter shortly referred to as a rough/finemovement stage), or a configuration can be employed where a head isprovided in stage main section 91 (rough movement stage) so as tomeasure a position of stage main section 91 (rough movement stage) usingthe head and to measure relative displacement of the rough/fine movementstage with another sensor.

When wafer stage WST1 and WST2 are located within the exposure timemovement area previously described, head 60 ₁ configures two-dimensionalencoders 70 ₁ and 71 ₁ (refer to FIG. 6) which irradiate a measurementbeam (measurement light) on (section 21 ₁ of) scale plate 21, receivethe diffraction beam from the grating whose periodical direction is in a135 degrees direction, or in other words, whose periodical direction isin a −45 degrees (hereinafter simply referred to as a −45 degreesdirection), with the X-axis serving as a reference formed on the surface(lower surface) of scale plate 21, and measure the position of wafertables WTB1 and WTB2 in the −45 degrees direction and in the Z-axisdirection. Similarly, heads 60 ₂ to 60 ₄ each configure two-dimensionalencoders 70 ₂ to 70 ₄ and 71 ₂ to 71 ₄ (refer to FIG. 6) which irradiatea measurement beam (measurement light) on (sections 21 ₂ to 21 ₄ of)scale plate 21, respectively, receive a diffraction beam from thegrating whose periodical direction is in a 225 degrees direction, or inother words, whose periodical direction is in a +45 degrees (hereinaftersimply referred to as a 45 degrees direction) with the X-axis serving asa reference, a 315 degrees direction, or in other words, whoseperiodical direction is in a −45 degrees direction with the X-axisserving as a reference, and a 45 degrees direction, formed on thesurface (lower surface) of scale plate 21, and measure the position inthe 225 degrees (45 degrees) direction and in the Z-axis direction, theposition in the 315 degrees (−45 degrees) direction and the Z-axisdirection, and the position in the 45 degrees direction and the Z-axisdirection of wafer tables WTB1 and WTB2.

Further, when wafer stage WST1 and WST2 are located within themeasurement time movement area previously described, head 60 ₁configures two-dimensional encoders 70 ₁ and 71 ₁ (refer to FIG. 6)which irradiate a measurement beam (measurement light) on (section 22 ₁of) scale plate 22, receive the diffraction beam from the grating whoseperiodical direction is in a 135 degrees direction (−45 degreesdirection) with the X-axis serving as a reference formed on the surface(lower surface) of scale plate 22, and measures the position of wafertables WTB1 and WTB2 in the 135 degrees direction and in the Z-axisdirection. Similarly, heads 60 ₂ to 60 ₄ configure two-dimensionalencoders 70 ₂ to 70 ₄ and 71 ₂ to 71 ₄ (refer to FIG. 6) which irradiatea measurement beam (measurement light) on (sections 22 ₂ to 22 ₄ of)scale plate 22, respectively, receive a diffraction beam from thegrating whose periodical direction is in a 225 degrees direction (45degrees direction), a 315 degrees direction (−45 degrees direction), anda 45 degrees direction with the X-axis serving as a reference, formed onthe surface (lower surface) of scale plate 22, and measure the positionof wafer tables WTB1 and WTB2 in the 225 degrees direction (45 degreesdirection) and in the Z-axis direction, the 315 degrees direction (−45degrees direction) and the Z-axis direction, and the 45 degreesdirection and the Z-axis direction.

As it can be seen from the description above, in this embodiment,regardless of irradiating the measurement beam (measurement light)either on scale plate 21 or 22, or in other words, regardless of whetherwafer stages WST1 and WST2 are located in the exposure time movementarea or the measurement time movement area, heads 60 ₁ to 60 ₄ configuretwo-dimensional encoder 70 ₁ to 70 ₄ along with the scale plates onwhich the measurement beam (measurement light) is irradiated, and heads60 ₁ to 60 ₄ on wafer stage WST2 are to configure two-dimensionalencoders 71 ₁ to 71 ₄, along with the scale plates on which themeasurement beams (measurement lights) are irradiated.

The measurement values of each of the two-dimensional encoders(hereinafter shortly referred to as an encoder as appropriate) 70 ₁ to70 ₄, and 71 ₁ to 71 ₄ are supplied to main controller 20 (refer to FIG.6). Main controller 20 obtains the positional information of wafer tableWTB1 and WTB2 within the exposure time movement area including the arearight under projection optical system PL, based on the measurementvalues of at least three encoders (in other words, at least threeencoders that output effective measurement values) which face the lowersurface of (sections 21 ₁ to 21 ₄ configuring) scale plate 21 on whichthe two-dimensional diffraction grating RG is formed. Similarly, maincontroller 20 obtains the positional information of wafer table WTB1 andWTB2 within the measurement time movement area including the area rightunder alignment system ALG, based on the measurement values of at leastthree encoders (in other words, at least three encoders that outputeffective measurement values) which face the lower surface of (sections22 ₁ to 22 ₄ configuring) scale plate 22 on which the two-dimensionaldiffraction grating RG is formed.

Further, in exposure apparatus 100 of the embodiment, the position ofwafer stages WST1 and WST2 (wafer tables WTB1 and WTB2) can be measuredwith wafer interferometer system 18 (refer to FIG. 6), independentlyfrom encoder systems 70 and 71. Measurement results of waferinterferometer system 18 are used secondarily such as when correcting(calibrating) a long-term fluctuation (for example, temporal deformationof the scale) of the measurement results of encoder systems 70 and 71,or as backup at the time of output abnormality in encoder systems 70 and71. Incidentally, details on wafer interferometer system 18 will beomitted.

Alignment system ALG is an alignment system of an off-axis method placedon the +X side of projection optical system PL away by a predetermineddistance, as shown in FIG. 1. In the embodiment, as alignment systemALG, as an example, an FIA (Field Image Alignment) system is used whichis a type of an alignment sensor by an image processing method thatmeasures a mark position by illuminating a mark using a broadband (awide band wavelength range) light such as a halogen lamp and performingimage processing of the mark image. The imaging signals from alignmentsystem ALG are supplied to main controller 20 (refer to FIG. 6), via analignment signal processing system (not shown).

Incidentally, alignment system ALG is not limited to the FIA system, andan alignment sensor, which irradiates a coherent detection light to amark and detects a scattered light or a diffracted light generated fromthe mark or makes two diffracted lights (for example, diffracted lightsof the same order or diffracted lights being diffracted in the samedirection) generated from the mark interfere and detects an interferencelight, can naturally be used alone or in combination as needed. Asalignment system ALG, an alignment system having a plurality ofdetection areas like the one disclosed in, for example, U.S. PatentApplication Publication No. 2008/0088843 can be employed.

Moreover, in exposure apparatus 100 of the embodiment, a multiple pointfocal point position detection system (hereinafter shortly referred toas a multipoint AF system) AF (not shown in FIG. 1, refer to FIG. 6) bythe oblique incidence method having a similar configuration as the onedisclosed in, for example, U.S. Pat. No. 5,448,332 and the like, isarranged at the measurement station together with alignment system ALG.At least a part of a measurement operation by the multipoint AF systemAF is performed in parallel with the mark detection operation byalignment system ALG, and the positional information of the wafer tableis also measured during the measurement operation by the encoder systempreviously described. Detection signals of multipoint AF system AF aresupplied to main controller 20 (refer to FIG. 6) via an AF signalprocessing system (not shown). Main controller 20 detects positionalinformation (step information/unevenness information) of the wafer Wsurface in the Z-axis direction based on the detection signals ofmultipoint AF system AF and the measurement information of the encodersystem previously described, and in the exposure operation, performs aso-called focus leveling control of wafer W during the scanning exposurebased on prior detection results and the measurement information(positional information in the Z-axis, the θx and θy directions) of theencoder system previously described. Incidentally, multipoint AF systemcan be arranged within the exposure station in the vicinity ofprojection unit PU, and at the time of exposure operation, the so-calledfocus leveling control of wafer W can be performed by driving the wafertable while measuring the surface position information (unevennessinformation) of the wafer surface.

In exposure apparatus 100, furthermore, above reticle R, a pair ofreticle alignment detection systems 13A and 13B (not shown in FIG. 1,refer to FIG. 6) of a TTR (Through The Reticle) method which uses lightof the exposure wavelength, as is disclosed in, for example, U.S. Pat.No. 5,646,413 and the like, is arranged. Detection signals of reticlealignment systems 13A and 13B are supplied to main controller 20 via analignment signal processing system (not shown). Incidentally, reticlealignment can be performed using an aerial image measuring instrument(not shown) provided on wafer stage WST, instead of the reticlealignment system.

FIG. 6 is a block diagram showing a partially omitted control systemrelated to stage control in exposure apparatus 100. This control systemis mainly configured of main controller 20. Main controller 20 includesa so-called microcomputer (or workstation) consisting of a CPU (CentralProcessing Unit), ROM (Read Only Memory), RAM (Random Access Memory) andthe like, and has overall control over the entire apparatus.

In exposure apparatus 100 configured in the manner described above, whenmanufacturing a device, main controller 20 moves one of wafer stagesWST1 and WST2 on which the wafer is loaded within the measurementstation (measurement time movement area), and the measurement operationof the wafer by alignment system ALG and multipoint AF system isperformed. More specifically, in the measurement time movement area onthe wafer held by one of wafer stages WST1 and WST2, mark detectionusing alignment system ALG, or the so-called wafer alignment (such asEnhanced Global Alignment (EGA) disclosed in, for example, U.S. Pat. No.4,780,617 and the like) and measurement of the surface position(step/unevenness information) of the wafer using the multipoint AFsystem are performed. On such alignment, encoder system 70 (encoders 70₁ to 70 ₄) or encoder system 71 (encoders 71 ₁ to 71 ₄) obtains(measures) the positional information of wafer stages WST1 and WST2 indirections of six degrees of freedom (X, Y, Z, θx, θy, and θz).

After the measurement operation such as the wafer alignment and thelike, one of the wafer stages (WST1 or WST2) is moved to exposure timemovement area, and main controller 20 performs reticle alignment and thelike in a procedure (a procedure disclosed in, for example, U.S. Pat.No. 5,646,413 and the like) similar to a normal scanning stepper, usingreticle alignment systems 13A and 13B, fiducial mark plates (not shown)on the wafer table (WTB1 or WTB2) and the like.

Then, main controller 20 performs an exposure operation by thestep-and-scan method, based on the measurement results of the waferalignment and the like, and a pattern of reticle R is transferred ontoeach of a plurality of shot areas on wafer W. The exposure operation bythe step-and-scan method is performed by alternately repeating ascanning exposure operation where synchronous movement of reticle stageRST and wafer stage WST1 or WST2 is performed, and a movement (stepping)operation between shots where wafer stage WST1 or WST2 is moved to anacceleration starting position for exposure of the shot area. At thetime of the exposure operation, encoder system 70 (encoders 70 ₁ to 70₄) or encoder system 71 (encoders 71 ₁ to 71 ₄) obtains (measures) thepositional information of one of the wafer stages WST1 or WST2, indirections of six degrees of freedom (X, Y, Z, θx, θy, and θz).

Further, exposure apparatus 100 of the embodiment is equipped with twowafer stages WST1 and WST2. Therefore, in parallel with performing anexposure by the step-and-scan method with respect to the wafer loaded onone of the wafer stages, such as, for example, wafer stage WST1, aparallel processing operation is performed in which wafer alignment andthe like is performed on the wafer mounted on the other stage WST2.

In exposure apparatus 100 of the embodiment, as is previously described,main controller 20 obtains (measures) the positional information ofwafer stage WST1 in directions of six degrees of freedom (X, Y, Z, θx,θy, and θz) using encoder system 70 (refer to FIG. 6), within both theexposure time movement area and the measurement time movement area.Further, main controller 20 obtains (measures) the positionalinformation of wafer stage WST2 in directions of six degrees of freedom(X, Y, Z, θx, θy, and θz) using encoder system 71 (refer to FIG. 6),within both the exposure time movement area and the measurement timemovement area.

Now, the principles of position measurement in directions of threedegrees of freedom (also shortly referred to as the X-axis direction,the Y axis direction and the θz direction (X, Y, θz)) within the XYplane by encoder systems 70 and 71 are further described. Here,measurement results or measurement values of encoder heads 60 ₁ to 60 ₄or encoders 70 ₁ to 70 ₄ refer to measurement results of encoder heads60 ₁ to 60 ₄ or encoders 70 ₁ to 70 ₄ in the measurement direction whichis not in the Z-axis direction.

In the embodiment, by employing a configuration and an arrangement ofencoder heads 60 ₁ to 60 ₄ and scale plate 21 as is previouslydescribed, at least three of the encoders head 60 ₁ to 60 ₄ constantlyface (corresponding sections 21 ₁ to 21 ₄ of) scale plate 21 within theexposure time movement area.

FIGS. 7 and 13 show a relation between a placement of encoder heads 60 ₁to 60 ₄ on wafer stage WST1 and each of the sections 21 ₁ to 21 ₄ ofscale plate 21, and measurement areas A₀ to A₄ of encoder system 70.Incidentally, because the configuration of wafer stage WST2 is similarto wafer stage WST1, the description here will be made only on waferstage WST1.

When the center (coincides with the center of the wafer) of wafer stageWST1 is located in the exposure time movement area, and within a firstarea A₁ which is an area on the +X and +Y sides with respect to exposurecenter (center of exposure area IA) P (an area within a first quadrantwhose origin is exposure center P (except for area A₀)), heads 60 ₄, 60₁, and 60 ₂ on wafer stage WST1 face sections 21 ₄, 21 ₁, and 21 ₂ ofscale plate 21, respectively. In the first area A₁, effectivemeasurement values are sent to main controller 20 from heads 60 ₄, 60 ₁,and 60 ₂ (encoders 70 ₄, 70 ₁, and 70 ₂). Incidentally, the position ofwafer stages WST1 and WST2 in the description below, will refer to theposition in the center of the wafer stages (coincides with the center ofthe wafer). In other words, instead of using the description of theposition in the center of wafer stages WST1 and WST2, the descriptionthe position of wafer stages WST1 and WST2 will be used.

Similarly, when wafer stage WST1 is located in the exposure timemovement area, and also within a second area A₂, which is an area (anarea (except for area A₀) within the second quadrant whose origin isexposure center P) on the −X side and also on the +Y side with respectto exposure center P, heads 60 ₁, 60 ₂, and 60 ₃ face sections 21 ₁, 21₂, and 21 ₃ of scale plate 21, respectively. When wafer stage WST1 islocated in the exposure time movement area, and also within a third areaA₃, which is an area (an area (except for area A₀) within the thirdquadrant whose origin is exposure center P) on the −X side and also onthe −Y side with respect to exposure center P, heads 60 ₂, 60 ₃, and 60₄ face sections 21 ₂, 21 ₃, and 21 ₄ of scale plate 21, respectively.When wafer stage WST1 is located in the exposure time movement area, andalso within a fourth area A₄, which is an area (an area (except for areaA₀) within the fourth quadrant whose origin is exposure center P) on the+X side and also on the −Y side with respect to exposure center P, heads60 ₃, 60 ₄, and 60 ₁ face sections 21 ₃, 21 ₄, and 21 ₁ of scale plate21, respectively.

In the embodiment, as well as a condition (A≧a_(i)+2t, B≧b_(i)+20 forthe configuration and placement of encoder heads 60 ₁ to 60 ₄ and scaleplate 21 previously described, condition A≧a_(i)+W+2t, B≧b_(i)+L+2t isadded, taking into consideration the size (W, L) of the shot area on thewafer in which the pattern is formed. In this case, W and L are thewidth of the shot area in the X-axis direction and the Y axis direction,respectively. W and L are equal to the distance of the scanning exposuresection and the distance of stepping in the X-axis direction,respectively. Under this condition, as shown in FIGS. 7 and 13, in thecase wafer stage WST1 is positioned within a cross-shaped area A₀ (anarea whose longitudinal direction is in the Y-axis direction and has awidth A−a_(i)−2t and an area an area whose longitudinal direction is inthe X-axis direction and has a width B−b_(i)−2t that pass throughexposure center P (hereinafter referred to as a zeroth area)) in whichexposure position P serves as the center, all of the heads 60 ₁ to 60 ₄on wafer stage WST1 face scale plate 21 (sections 21 ₁ to 21 ₄corresponding to the heads). Accordingly, within the zeroth area A₀,effective measurement values from all of the heads 60 ₁ to 60 ₄(encoders 70 ₁ to 70 ₄) are sent to main controller 20. Incidentally, inthe embodiment, in addition to the conditions (A≧a_(i)+2t, B≧b_(i)+20described above, condition A≧a_(i)+W+2t, B≧b_(i)+L+2t may be addedtaking into consideration the size (W, L) of the shot area on the waferin which the pattern is formed. In this case, W and L are the width ofthe shot area in the X-axis direction and the Y axis direction,respectively. W and L are equal to the distance of the scanning exposuresection and the distance of stepping in the X-axis direction,respectively.

Main controller 20 computes the position (X, Y, θz) of wafer stage WST1in the XY plane, based on measurement results of heads 60 ₁ to 60 ₄(encoders 70 ₁ to 70 ₄). In this case, measurement values (eachdescribed as C₁ to C₄) of encoders 70 ₁ to 70 ₄ depend upon the position(X, Y, θz) of wafer stage WST1 as in formulas (1) to (4) below.

C ₁=−(cos θz+sin θz)X/√2+(cos θz−sin θz)Y/√2+√2p sin θz  (1)

C ₂=−(cos θz−sin θz)X/√2−(cos θz+sin θz)Y/√2+√2p sin θz  (2)

C ₃=(cos θz+sin θz)X/√2−(cos θz−sin θz)Y/√2+√2p sin θz  (3)

C ₄=(cos θz−sin θz)X/√2+(cos θz+sin θz)Y/√2+√2p sin θz  (4)

However, as shown in FIG. 5, p is the distance of the head in the X-axisand the Y-axis directions from the center of wafer table WTB1 (WTB2).

Main controller 20 specifies three heads (encoders) facing scale plate21 according to areas A₀ to A₄ where wafer stage WST1 is positioned andforms a simultaneous equation by choosing from the formulas (1) to (4)above the formula which the measurement values of the three headsfollow, and by solving the simultaneous equation using the measurementvalues of the three heads (encoders), computes the position (X, Y, θz)of wafer sage WST1 in the XY plane. For example, when wafer stage WST1is located in the first area A₁, main controller 20 forms a simultaneousequation from formulas (1), (2) and (4) that measurement values of heads60 ₁, 60 ₂, and 60 ₄ (encoders 70 ₁, 70 ₂, and 70 ₄) follow, and solvesthe simultaneous equation by substituting the measurement values of eachof the heads into the left side of formulas (1), (2) and (4),respectively.

Incidentally, in the case wafer stage WST1 is located in the zeroth areaA₀, main controller 20 can randomly select three heads from heads 60 ₁to 60 ₄ (encoders 70 ₁ to 70 ₄). For example, after the first waferstage WST1 has moved from the first area to the zeroth area, heads 60 ₁,60 ₂, and 60 ₄ (encoders 70 ₁, 70 ₂, and 70 ₄) corresponding to thefirst area are preferably selected.

Main controller 20 drives (position control) wafer stage WST1 within theexposure time movement area, based on the computation results (X, Y, θz)above.

In the case wafer stage WST1 is located within measurement time movementarea, main controller 20 measures the positional information indirections of three degrees of freedom (X, Y, θz), using encoder system70. The measurement principle and the like, here, is the same as in thecase when wafer stage WST1 is located within the measurement timemovement area, except for the point where exposure center P is replacedwith the detection center of alignment system ALG, and (sections 21 ₁ to21 ₄ of) scale plate 21 is replaced with (sections 22 ₁ to 22 ₄ of)scale plate 22.

Furthermore, main controller 20 switches and uses three heads thatincludes at least one different head, out of heads 60 ₁ to 60 ₄ thatface scale plates 21 and 22, according to the position of wafer stagesWST1 and WST2. In this case, when switching the encoder head, a linkageprocess to secure the continuity of the position measurement results ofthe wafer stage is performed, as is disclosed in, for example, U.S.Patent Application Publication No. 2008/0094592 and the like.

Now, switching and linkage process of heads 60 ₁ to 60 ₄ at the time ofexposure operation by the step-and-scan method will be furtherdescribed.

As a first example, an exposure operation with respect to wafer W₁ shownin FIG. 7 will be described. In this case, on wafer W₁, as an example, atotal of 36 shot areas S₁ to S₃₆, which are arranged in an even numberin the X-axis direction and an odd number in the Y-axis direction, areto be arranged, as is shown enlarged in FIG. 8.

An exposure by the step-and-scan method is performed with respect towafer W₁, along a path shown in FIG. 9. Incidentally, the path in FIG. 9shows the track of exposure center (the center of exposure area IA) Pwhich passes over each of the shot areas. The solid line portion of thistrack shows a movement track of exposure center P on scanning exposureof each of the shots, and the dotted line portion (broken line portion)shows a step movement track of exposure center P between adjacent shotareas in the scanning direction and in a direction besides the scanningdirection. Incidentally, although in actual, exposure center P is fixedand the wafer moves in a direction opposite to the path shown in FIG. 9,for the sake of convenience, the exposure center is to move with respectto a fixed wafer in the description.

In exposure apparatus 100 of the embodiment, three heads of heads 60 ₁to 60 ₄ opposing scale plate 21 are switched and used, in response tothe position of wafer stage WST1. Accordingly, when wafer stage WST1moves from one of the areas A₁ to A₄ shown in FIG. 7 to another area viaarea A₀, the head which is to be used is switched. Therefore, in FIG. 9,overlaying the track of exposure center P on wafer W₁, areas B₀ to B₄are shown which correspond to the set of heads opposing scale plate 21when wafer stage WST1 is located at the position in the track ofexposure center P.

Areas B₀ to B₄ in FIG. 9 correspond to movement areas A₀ to A₄ of waferstage WST1 in FIG. 7, respectively. For example, when performingscanning exposure of the shot areas within area B₁, or when performing astep movement to the next shot area, wafer stage WST1 moves within areaA_(i). Accordingly, when exposure center P is located in area B₁, heads60 ₄, 60 ₁, and 60 ₂ face scale plate 21. Similarly, when exposurecenter P is located in areas B₂, B₃, B₄, and B₀, heads 60 ₁, 60 ₂, and60 ₃, heads 60 ₂, 60 ₃, and 60 ₄, heads 60 ₃, 60 ₄, and 60 ₁, and all ofthe heads 60 ₁ to 60 ₄ face scale plate 21, respectively.

Accordingly, exposure center P moves over the track shown in FIG. 9 bythe scanning exposure of the shot area or the step movement between shotareas, and the head which is to be used is switched when exposure centerP moves from one of the areas B₁ to B₄ to another area via area B₀.Therefore, in FIG. 9, occurrence places of the switching of the headswith respect to wafer W are shown by a double circle.

For example, first of all, after exposure center P performs exposureprocessing on the first shot area S₁ to the third shot area S₃ and hasmoved from area B₁ to area B₀, switching of the head (a first switching)occurs when exposure processing of the fourth shot area S₄ within areaB₀ shown inside circle C₁ is performed and exposure center P is steppedto the fifth shot area S₅ within area B₂. Now, as is previouslydescribed, when exposure center P is located in areas B₁, B₀, and B₂,heads 60 ₀, 60 ₁, and 60 ₂, all of the heads 60 ₁ to 60 ₄, heads 60 ₁,60 ₂, and 60 ₃ face scale plate 21, respectively. Accordingly, in thefirst switching, the heads to be used are switched from heads 60 ₄, 60₁, and 60 ₂ to heads 60 ₁, 60 ₂, and 60 ₃.

FIG. 10A shows an enlarged view of the inside of circle C₁ in FIG. 9used to explain the details of the first switching, and FIG. 10B shows atemporal change of velocity Vy in the Y-axis direction of wafer stageWST1 after the first switching.

After the exposure processing of the third shot area S₃ has beenperformed, main controller 20 drives (position control) wafer stage WST1based on measurement results of heads 60 ₄, 60 ₁, and 60 ₂ (encoders 70₄, 70 ₁, and 70 ₂), so that exposure center P is moved to anacceleration starting position e₄ to expose the fourth shot area S₄.When exposure center P reaches acceleration starting position e₄, maincontroller 20 starts a synchronous movement of wafer stage WST1 (waferW₁) and reticle stage RST (reticle R). In other words, main controller20 accelerates and drives wafer stage WST1, and concurrently drivesreticle stage RST which follows the movement of wafer stage WST1, in adirection opposite to wafer stage WST1 also at a velocity which is amultiple of the inverse number of projection magnification β of thevelocity of wafer stage WST1. As shown in FIG. 10B, the velocity of bothstages WST1 and WST2 becomes constant, after an acceleration time T_(a)has passed from the beginning of acceleration (time t₄).

After the acceleration has been completed, for a settling time T_(b)until the beginning of exposure, main controller 20 drives reticle stageRST so that reticle stage RST follows wafer stage WST1 until adisplacement error between wafer W₁ and reticle R becomes apredetermined relation (approximately zero).

After settling time T_(b), main controller 20 drives wafer stage WST1 ina constant manner, based on measurement results of heads 60 ₄, 60 ₁, and60 ₂ (encoders 70 ₄, 70 ₁, and 70 ₂). This allows exposure area IA(exposure center P) to move at a constant velocity from the −Y edge tothe +Y edge of shot area S4 as is shown in FIG. 10A during exposure timeT_(c), and scanning exposure of shot area S₄ is performed. During thescanning exposure, the synchronous movement state at a constant velocityof wafer W₁ and reticle R is maintained.

After the exposure has been completed, wafer stage WST1 moves in aconstant velocity during a uniform velocity overscan time (postsettlingtime) T_(d). During this movement, as is shown in FIG. 10A, exposurecenter P passes through the first switching position P₁ on the +Y sideof shot area S₄ at a constant velocity. At this point, main controller20 switches the heads to be used from heads 60 ₄, 60 ₁, and 60 ₂(encoders 70 ₄, 70 ₁, and 70 ₂) to heads 60 ₁, 60 ₂, and 60 ₃ (encoders70 ₁, 70 ₂, and 70 ₃). Now, main controller 20 performs a linkageprocess in order to secure the continuity of measurement results of theposition of wafer stage WST1 before and after the switching. In otherwords, main controller 20 resets measurement values C₃ of head 60 ₃which is to be newly used after the switching, so that measurementresults (X′, Y′, θz′) of the position of wafer stage WST1 obtained frommeasurement values of heads 60 ₁, 60 ₂, and 60 ₃ coincide withmeasurement results (X, Y, θz) of wafer stage WST1 obtained frommeasurement values of heads 60 ₄, 60 ₁, and 60 ₂. Details of thislinkage process will be describer further in the description.

After the switching, main controller 20, decelerates and drives waferstage WST1, based on the measurement results of heads 60 ₁, 60 ₂, and 60₃ (encoders 70 ₁, 70 ₂, and 70 ₃) during a deceleration overscan timeT_(e). At the same time, reticle stage RST is also decelerated.Incidentally, in the deceleration overscan time T_(e), wafer stage WST1is moved in the X-axis direction as well, in parallel with being movedin the Y-axis direction. This makes exposure center P draw a U-shapedtrack from the +Y edge of shot area S₄ and perform a step movementtoward the next shot area within area B₂.

After the deceleration of wafer stage WST1 has been completed, maincontroller 20 continues to drive wafer stage WST1 and reticle stage RSTas is previously described, however, in opposite directions, and exposesthe next shot area S₅.

The measurement results of encoder system 70 (71) include a measurementerror caused by a production error of the scale and the like.

Now, in the following description, the four heads will be abstractlydescribed as Enc1, Enc2, Enc3, and Enc4 so as to describe the principleof the switching of the heads and the linkage process.

FIG. 11A shows the (track of) a temporal change of a position coordinate(X, Y, θz) of wafer stage WST1 computed from the measurement values ofencoders Enc1, Enc2, and Enc3, and a position coordinate (X′, Y′, θz′)of wafer stage WST1 computed from the measurement values of encodersEnc2, Enc3, and Enc4, before and after the switching of heads from Enc1,Enc2, and Enc3 to Enc2, Enc3, and Enc4. The track of the measurementresults of the position of wafer stage WST1 fluctuates minutely bymeasurement errors due to the production error of the scale and thelike. Therefore, in a simple linkage process like the one disclosed inU.S. Patent Application Publication No. 2008/0094592 and the like,measurement values of encoder Enc4 (in this case, measurement value C₄of head 60 ₄) which is to be newly used will be reset taking in themeasurement errors as well. In the embodiment, a linkage process whichprevents such a situation from occurring is employed.

Next, a principle of a linkage process performed in exposure apparatus100 of the embodiment will be described. In the embodiment, maincontroller 20 controls the position coordinates of wafer stage WST1 byan interval of, for example, 96 μsec. At each control sampling interval,a position servo control system (part of main controller 20) updates thecurrent position of wafer stage WST1, computes thrust command values andthe like to position the stage to a target position, and outputs theresults to wafer stage drive system 27. As is previously described, thecurrent position of wafer stage WST1 is computed using three measurementvalues of heads 60 ₁ to 60 ₄ (encoders 70 ₁ to 70 ₄) which configureencoder system 70. The measurement values of these heads (encoders) aremonitored at a time interval (measurement sampling interval) muchshorter than the control sampling interval.

FIG. 12 shows an outline of a drive (position control) of wafer stageWST, switching of heads 60 ₁ to 60 ₄ (encoders 70 ₁ to 70 ₄), and alinkage process which comes with the switching, based on the measurementresults of encoder system 70. Reference code CSCK in FIG. 12 indicatesthe generation timing of a sampling clock (a control clock) of theposition control of wafer stage WST1, and reference code MSCK indicatesa generation timing of a sampling clock (a measurement clock) of themeasurement of the encoder.

Main controller 20 monitors the measurement values of (the four encodersEnc1, Enc2, Enc3, and Enc4 which configure) encoder system 70 for eachcontrol clock (CSCK).

At the time of the first switching, encoders Enc1, Enc2, Enc3, and Enc4correspond to heads 60 ₄, 60 ₁, 60 ₂, and 60 ₃ (encoders 70 ₄, 70 ₁, 70₂, and 70 ₃), respectively.

At the time of the control clock, main controller 20 computes a positioncoordinate (X, Y, θz) of wafer stage WST1 using a simultaneous equationconsisting of formulas (1) to (3) which correspond to the measurementvalues of encoders Enc1, Enc2, and Enc3 like the time of the firstcontrol clock, as well as compute a position coordinate (X′, Y′, θz′) ofwafer stage WST1 using the measurement values of encoders Enc2, Enc3,and Enc4 which are to be used after the switching.

Main controller 20 outputs a stage position coordinate (X, Y, θz)computed from the measurement values of encoders Enc1, Enc2, and Enc3 towafer stage drive system 27 as a stage coordinate system for servocontrol and drives wafer stage WST1, until the scanning exposure(exposure time Tc) of shot area S₄ has been completed. After theexposure has been completed, main controller 20 switches from encodersEnc1, Enc2, and Enc3 to encoders Enc2, Enc3, and Enc4, at the time ofthe third control clock during uniform velocity overscan time(postsettling time) Td.

As shown in FIG. 11A, the continuity of the stage position coordinate isnot satisfied in the simple linkage process, due to the measurementerrors caused by the production error of the scale and the like.Therefore, in parallel with the scanning exposure to shot area S₄, or inother words, driving wafer stage WST1 in a constant manner for a part Q1of the scanning exposure section shown in FIG. 10A, main controller 20performs a preprocessing (also referred to as a linkage computing) foreach control clock (CSCK). In other words, main controller 20 obtains adifference between position coordinate (X, Y, θz) and positioncoordinate (X′, Y′, θz′) as shown in FIG. 12, and furthermore obtains amoving average MA_(K) {(X, Y, θz)−(X′, Y θz′)} of the difference for apredetermined clock number K, which is held as a coordinate offset O. InFIG. 12, the calculation of the moving average is indicated by referencecode MA_(K).

Incidentally, moving average MA_(K) (X, Y, θz) and MA_(K) (X′, Y′, θz′)can be obtained for a predetermined clock number K with respect toposition coordinate (X, Y, θz) and the position coordinate (X′, Y′,θz′), respectively, and a difference MA_(K)(X, Y, θz)−MA_(K)(X Y′, θz′)can be held as coordinate offset O.

Main controller 20 performs a linkage process in the case of switching.In other words, main controller 20 adds the coordinate offset O held atthe time of the second control clock just before to position coordinate(X′, Y′, θz′) of wafer stage WST1 computed from the measurement valuesof encoders Enc2, Enc3, and Enc4 at the time of the third control clock,so that the position coordinate coincides with a position coordinate (X,Y, θz) of wafer stage WST1 computed by the measurement values ofencoders Enc1, Enc2, and Enc3 at the time of the control clock justbefore (in this case, the time of the second control clock). Theposition coordinate {(X Y′, θz′)+O} to which offset cancellation hasbeen applied is substituted in one of the formulas (1) to (4) that themeasurement values of encoder Enc4 follow, so as to compute themeasurement values of encoder Enc4, which are set as the measurementvalues of Enc4. FIG. 12 shows this linkage process as code CH.

When the linkage process above is performed, it should be confirmed thatthe value of coordinate offset O is sufficiently stable for the mostrecent predetermined clock number. Furthermore, as is previouslydescribed, position coordinate (X, Y, θz) of wafer stage WST1 computedfrom the measurement values of encoder system 70 fluctuates minutelywith respect to the true position by measurement errors due to theproduction error of the scale and the like. Therefore, the linkageprocess should be performed at a timing (at the time of clockgeneration) where the difference between position coordinate (X, Y, θz)of wafer stage WST1 computed from the measurement values of encodersEnc1, Enc2, and Enc3 and position coordinate (X Y′, θz′) of wafer stageWST1 computed from the measurement values of encoders Enc2, Enc3, andEnc4 coincides or almost coincides with coordinate offset O which issufficiently stable.

By the linkage process described so far, the continuity of the positioncoordinate of the wafer stage computed before and after the switching issecured, as shown in FIG. 11B.

Incidentally, the linkage process is not limited to the case ofcorrecting the measurement values of the heads after switching asdescribed above, and such other process can also be employed. Forexample, other methods can also be applied, such as driving (performingposition control of) the wafer stage while adding an offset to thecurrent position or the target position of the wafer stage with themeasurement errors serving as an offset, or correcting the reticleposition only by the measurement error.

After the time of the fourth control clock in FIG. 12 after theswitching, main controller 20 outputs position coordinate (X′, Y′, θz′)computed from the measurement values of encoders Enc2, Enc3, and Enc4 towafer stage drive system 27 as a stage coordinate for servo control, anddrives and controls wafer stage WST1.

Incidentally, in the first switching described above, the head to beused was switched after scanning exposure of the fourth area S₄ withinarea B₀ was performed, before the step movement to the fifth shot areaS₅ within area B₂ is performed. Now, in the arrangement of the shot areaon wafer W₁ shown in FIG. 7, the third shot area S₃ is also included inarea B₀ as shown in FIG. 9. Therefore, as shown in FIG. 10C, the head tobe used can be switched after scanning exposure of the third area S₃within area B₀ has been performed, before the step movement to thefourth shot area S₄ is performed. In this case, after the scanningexposure of the third shot area S₃ has been performed driving waferstage WST1 in a constant manner for a part of the scanning exposuresection Q1′ with respect to shot area S₃, concurrently with the linkagecomputing described above being performed, the heads to be used areswitched from heads 60 ₄, 60 ₁, and 60 ₂ to heads 60 ₁, 60 ₂, and 60 ₃when wafer stage WST1 passes through a switching occurrence position P₁′on the −Y side of the third shot area S₃ at a constant speed. In suchcase, main controller 20 resets measurement value C₃ of head 60 ₃ whichis to be newly used after the linkage process, or in other words, afterthe switching, using coordinate offset O which is obtained by thelinkage computing, so that the continuity of the measurement results ofthe position of wafer stage WST1 before and after the switching issecured.

Similar to the first switching described above, after exposure center Pperforms exposure processing on the seventh shot area S₇ to the tenthshot area S₁₀ and has moved from area B₂ to area B₀, switching of thehead (a second switching) occurs when exposure processing of theeleventh shot area S₁₁ within area B₀ is performed and exposure center Pis stepped to the twelfth shot area S₁₂ within area B₁. In this case,the heads to be used are switched from heads 60 ₁, 60 ₂, and 60 ₃ toheads 60 ₄, 60 ₁, and 60 ₂.

Next, when a step-and-scan exposure is performed of the 15^(th) shotarea S₁₅ to the 22^(nd) shot area S₂₂ lined in the X-axis direction inthe center of the Y axis direction on wafer W₁, exposure center P movesbetween areas B₁ and B₄ or areas B₂ and B₃, via area B₀. Switching ofthe head (the third to the eleventh switching) occurs herein. Whenexposure center P moves between areas B₁ and B₄ via area B₀, the head tobe used is switched between heads 60 ₄, 60 ₁, and 60 ₂ and heads 60 ₃,60 ₄, and 60 ₁, and when exposure center P moves between areas B₂ andB₃, the head to be used is switched between heads 60 ₁, 60 ₂, and 60 ₃and heads 60 ₂, 60 ₃, and 60 ₄.

FIG. 10D shows an enlarged view of the inside of circle C₂ in FIG. 9,which is a view used to explain the details of the eighth and ninthswitching, representing the third to the eleventh switching. As it canbe seen from FIG. 10D, the 20^(th) shot area S₂₀ and the 21^(st) shotarea S₂₁ (and other shot areas; the 15^(th) shot area S₁₅ to the 19^(th)shot area S₁₉, and the 22^(nd) shot area S₂₂) are located in area B₀.The track of exposure center P steps over area B₀, and spreads out toareas B₂ and B₃. In other words, exposure center P steps over area B₀,and moves back and forth areas B₂ and B₃.

After the 19_(th) shot area S₁₉ has been exposed, main controller 20drives (controls the position of) wafer stage WST1 based on themeasurement results of heads 60 ₂, 60 ₃, and 60 ₄ (encoders 70 ₂, 70 ₃,and 70 ₄), and performs a step movement of exposure center P toward the20^(th) shot area S₂₀ along a path shown in a U-shape indicated by abroken line in FIG. 10D.

When exposure center P reaches acceleration starting position during thestep movement, main controller 20 starts acceleration (synchronousdrive) of wafer stage WST1 (wafer W₁) and reticle stage RST (reticle R).The velocity of both stages WST1 and RST becomes constant, after anacceleration time (T_(a)) has passed from the beginning of theacceleration.

Furthermore, during exposure time (T_(a)) after settling time (T_(b)),main controller 20 drives wafer stage WST1 in a constant manner, basedon measurement results of heads 60 ₂, 60 ₃, and 60 ₄ (encoders 70 ₂, 70₃, and 70 ₄). This allows exposure center P to move in a constantvelocity movement along a straight line path (scanning exposure path)indicated using a solid line in FIG. 10D. In other words, exposure areaIA (exposure center P) moves in a constant velocity from the +Y edge tothe −Y edge of shot area S₂₀, and scanning exposure of shot area S₂₀ isperformed.

In parallel with the scanning exposure of shot area S₂₀ described above,or to be exact, in parallel with driving wafer stage WST1 in a constantmanner for a part Q2 of the scanning exposure path with respect to shotarea S₂₀, main controller 20 performs the linkage computing previouslydescribed. After scanning exposure of the 20^(th) shot area S₂₀ has beenperformed, main controller 20 switches the heads to be used from heads60 ₂, 60 ₃, and 60 ₄ to heads 60 ₁, 60 ₂, and 60 ₃ when wafer stage WST1passes through a switching occurrence position P₂ on the −Y side of the20th shot area S20 at a constant speed. Here, main controller 20 resetsmeasurement value C₁ of head 60 ₁ which is to be newly used after thelinkage process previously described, or in other words, after theswitching, using coordinate offset O which is obtained by the linkagecomputing, so that the continuity of the measurement results of theposition of wafer stage WST1 before and after the switching is secured.

After the switching, main controller 20 drives (controls the positionof) wafer stage WST1 based on the measurement results of heads 60 ₁, 60₂, and 60 ₃ (encoders 70 ₁, 70 ₂, and 70 ₃), and performs a stepmovement toward the next shot area S₂₁. In this case, exposure center Pdraws a U-shaped track from the −Y edge of shot area S₂₀ and retreats toarea B₂ once, and then returns to area B₀ and moves toward the next shotarea S₂₀.

When exposure center P reaches acceleration starting position during thestep movement, main controller 20 starts acceleration (synchronousdrive) of wafer stage WST1 (wafer W₁) and reticle stage RST (reticle R).

Then, after acceleration time T_(a) and settling time T_(b) have passedfrom the beginning of the acceleration. main controller 20 drives waferstage WST1 in a constant manner along the straight line path (scanningexposure path) indicated by a solid line in FIG. 10D, based on themeasurement results of heads 60 ₁, 60 ₂, and 60 ₃ (encoders 70 ₁, 70 ₂,and 70 ₃). This allows exposure area IA (exposure center P) to move at aconstant velocity from the −Y edge to the +Y edge of shot area S₂₁, andscanning exposure of shot area S₂₁ is performed.

In parallel with the scanning exposure of shot area S₂₁ described above,or to be exact, in parallel with driving wafer stage WST1 in a constantmanner for a part Q3 of the scanning exposure path with respect to shotarea S₂₁, main controller 20 performs the linkage computing previouslydescribed. After scanning exposure of the 21^(st) shot area S₂₁ has beenperformed, main controller 20 switches the heads to be used from heads60 ₁, 60 ₂, and 60 ₃ to heads 60 ₂, 60 ₃, and 60 ₄ when wafer stage WST1passes through a switching occurrence position P₃ on the +Y side of the21⁴ shot area S₂₁ at a constant speed. Here, main controller 20 resetsmeasurement value C₄ of head 60 ₄ which is to be newly used after thelinkage process previously described, or in other words, after theswitching, using coordinate offset O which is obtained by the linkagecomputing, so that the continuity of the measurement results of theposition of wafer stage WST1 before and after the switching is secured.

After the switching, main controller 20 drives (controls the positionof) wafer stage WST1 based on the measurement results of heads 60 ₂, 60₃, and 60 ₄ (encoders 70 ₂, 70 ₃, and 70 ₄), and performs a stepmovement toward the next shot area S₂₂. In this case, exposure center Pdraws a U-shaped track from the +Y edge of shot area S₂₁ and retreats toarea B₃ once, and then returns to area B₀ and moves toward the next shotarea S₂₂.

Next, after exposure center P performs exposure processing on the23^(rd) shot area S₂₃ to the 26^(th) shot area S₂₆ and has moved fromarea B₃ to area B₀, switching of the head (a twelfth switching) occurswhen exposure processing of the 27^(th) shot area S₂₇ within area B₀ isperformed and exposure center P is stepped to the 28^(th) shot area S₂₈within area B₄. In this case, the heads to be used are switched fromheads 60 ₂, 60 ₃, and 60 ₄ to heads 60 ₃, 60 ₄, and 60 ₁. The detailsare similar to the first switching previously described.

Similarly, after exposure center P performs exposure processing on the31⁴ shot area S₃₁ to the 33^(rd) shot area S₃₃ and has moved from areaB₄ to area B₀, switching of the head (a thirteenth switching) occurswhen exposure processing of the 34^(th) shot area S₃₄ within area B₀ isperformed and exposure center P is stepped to the 35^(th) shot area S₃₅within area B₃. In this case, the heads to be used are switched fromheads 60 ₃, 60 ₄, and 60 ₁ to heads 60 ₂, 60 ₃, and 60 ₄. The details inthis case are also similar to the first switching previously described.

Due to the switching procedure and the linkage process described above,because switching of the heads do not occur during the scanning exposureof each shot area on the wafer in the exposure operation by thestep-and-scan method, sufficient overlay accuracy is maintained, and astable exposure processing of the wafer can be realized. Further,because the linkage computing is performed while wafer stage WST1 (WST2)moves at a constant speed during the scanning exposure, and the linkageprocess and the switching of the heads are performed using the resultsright after the scanning exposure, the continuity of the positionmeasurement results of the wafer stage before and after the switching ofthe heads is secured.

Next, as a second example, an exposure operation with respect to waferW₂ shown in FIG. 13 will be described. In this case, on wafer W₂, atotal of 38 shot areas S₁ to S₃₈, which are arranged in an odd number inthe X-axis direction and an even number in the Y-axis direction, are tobe arranged, as is shown enlarged in FIG. 14.

An exposure by the step-and-scan method is performed with respect towafer W2, along a path shown in FIG. 15. In FIG. 15, overlapping thepath, areas B0 to B4 corresponding to the set of heads that face scaleplate 21 when wafer stage WST1 is located at the position of exposurecenter P on the path and the occurrence place of the switching of theheads are shown. The notation in FIG. 15 is similar to the notation inFIG. 9.

First of all, after exposure center P performs exposure processing onthe first shot area S₁ and has moved from area B₁ to area B₀, switchingof the head (a first switching) occurs when exposure processing of thesecond shot area S₂ within area B₀ is performed and exposure center P isstepped to the third shot area S₃ within area B₂. Now, as is previouslydescribed, when exposure center P is located in areas B₁, B₀, and B₂,heads 60 ₄, 60 ₁, and 60 ₂, all of the heads 60 ₁ to 60 ₄, heads 60 ₁,60 ₂, and 60 ₃ face scale plate 21, respectively. Accordingly, in thefirst switching, the heads to be used are switched from heads 60 ₄, 60₁, and 60 ₂ to heads 60 ₁, 60 ₂, and 60 ₃. The details are similar tothe first switching with respect to wafer W₁ in the first examplepreviously described.

Similar to the first switching described above, after exposure center Pperforms exposure processing on the fourth shot area S₄ to the sixthshot area S₆ and has moved from area B₂ to area B₀, switching of thehead (a second switching) occurs when exposure processing of the seventhshot area S₇ within area B₀ is performed and exposure center P isstepped to the eighth shot area S₈ within area B₁. In this case, theheads to be used are switched from heads 60 ₁, 60 ₂, and 60 ₃ to heads60 ₄, 60 ₁, and 60 ₂.

Next, when a step-and-scan exposure is performed of the 11^(th) shotarea S₁₁ to the 19^(th) shot area S₁₉ lined in the X-axis direction inthe center of the Y axis direction (the third row) on wafer W₂, exposurecenter P moves between areas B₁ and B₄ or areas B₂ and B₃, via area B₀.Switching of the head (the third to the tenth switching) occurs herein.Similarly, when a step-and-scan exposure is performed of the 20^(th)shot area S₂₀ to the 28^(th) shot area S₂₈ lined in the X-axis directionin the fourth row, exposure center P moves between areas B₁ and B₄ orareas B₂ and B₃, via area B₀. Switching of the head (the eleventh to theeighteenth switching) occurs herein. When exposure center P movesbetween areas B₁ and B₄ via area B₀, the head to be used is switchedbetween heads 60 ₄, 60 ₁, and 60 ₂ and heads 60 ₃, 60 ₄, and 60 ₁, andwhen exposure center P moves between areas B₂ and B₃, the head to beused is switched between heads 60 ₁, 60 ₂, and 60 ₃ and heads 60 ₂, 60₃, and 60 ₄.

FIG. 16A shows an enlarged view of the inside of circle C₃ in FIG. 15,which is a view used to explain the details of the third and fourthswitching, representing the third to the eighteenth switching. As it canbe seen from FIG. 16A, the eleventh shot area S₁₁ and the twelfth shotarea S₁₂ are located on the border of area B₀ and area B₁. The track ofexposure center P steps over area B₀, and spreads out to areas B₁ andB₄. In other words, exposure center P steps over area B₀, and moves backand forth areas B₁ and B₄.

In this example, because the shot area subject to exposure is notcompletely included in area B₀, the detailed procedure of the third andthe fourth switching differs to some extent from the detailed procedureof the eighth and the ninth switching of wafer W₁ previously described.Therefore, details of the third and the fourth switching will bedescribed, placing an emphasis on the difference.

After the tenth shot area S₁₀ has been exposed, main controller 20drives (controls the position of) wafer stage WST1 based on themeasurement results of heads 60 ₄, 60 ₁, and 60 ₂ (encoders 70 ₄, 70 ₁,and 70 ₂), and performs a step movement of exposure center P toward theacceleration starting position for exposure of the eleventh shot areaS₁₁ along a path indicated by a broken line in FIG. 15.

After the step movement, main controller 20 starts the accelerationsynchronous drive of wafer stage WST1 (wafer W1) and reticle stage RST(reticle R). The velocity of both stages WST1 and RST becomes constant,after an acceleration time (T_(a)) has passed from the beginning of theacceleration.

Furthermore, during exposure time (T_(a)) After settling time (T_(b)),main controller 20 drives wafer stage WST1 in a constant manner, basedon measurement results of heads 60 ₄, 60 ₁, and 60 ₂ (encoders 70 ₄, 70₁, and 70 ₂). This allows exposure center P to move in a constantvelocity movement along a straight line path (scanning exposure path)indicated using a solid line in FIG. 16A. In other words, exposure areaIA (exposure center P) moves at a constant velocity from the −Y edge tothe +Y edge of shot area S₁₁, and scanning exposure of shot area S₁₁ isperformed.

In parallel with the scanning exposure of shot area S₁₁ previouslydescribed, or to be exact, in parallel with driving wafer stage WST1 ina constant manner for a part Q₅ of the scanning exposure path withrespect to shot area S₁₁, main controller 20 performs the linkagecomputing previously described, like the eighth and ninth switching withrespect to wafer W₁ previously described. After scanning exposure of theeleventh shot area S₁₁ has been performed, main controller 20 switchesthe heads to be used from heads 60 ₄, 60 ₁, and 60 ₂ to heads 60 ₃, 60₄, and 60 ₁ (the third switching) when wafer stage WST1 passes through aswitching occurrence position P₅ on the +Y side of the eleventh shotarea S₁₁ at a constant speed. Here, main controller 20 resetsmeasurement value C₃ of head 60 ₃ which is to be newly used after thelinkage process previously described, or in other words, after theswitching, using coordinate offset O which is obtained by the linkagecomputing, so that the continuity of the measurement results of theposition of wafer stage WST1 before and after the switching is secured.

After the switching, main controller 20 drives (controls the positionof) wafer stage WST1 based on the measurement results of heads 60 ₃, 60₄, and 60 ₁ (encoders 70 ₃, 70 ₄, and 70 ₁), and performs a stepmovement toward the next shot area S₁₂. In this case, exposure center Pdraws a U-shaped track from the +Y edge of shot area S₁₁ and retreats toarea B₄ once, and then returns to area B₀ and moves toward the next shotarea S₁₂.

When exposure center P reaches acceleration starting position during thestep movement, main controller 20 starts acceleration (synchronousdrive) of wafer stage WST1 (wafer W1) and reticle stage RST (reticle R)to perform exposure processing on shot area S₁₂. However, because shotarea S₁₂ is located on the border of area B₀ and area B₁, the heads needto be switched during the scanning exposure of the twelfth shot areaS₁₂. Therefore, in the fourth switching, the heads to be used areswitched from heads 60 ₃, 60 ₄, and 60 ₁ to heads 60 ₄, 60 ₁, and 60 ₂before scanning exposure of the twelfth shot area S₁₂ is performed.

In the fourth switching, while exposure center P performs a stepmovement from shot area S₁₁ to shot area S₁₂ along a U-shaped path priorto the switching, main controller 20 performs the linkage computingpreviously described concurrently with driving wafer stage WST1 in aconstant manner for part of a short straight line section Q₆ whichexposure center P passes during settling time T_(b). Before scanningexposure of the twelfth shot area S_(it), main controller 20 switchesthe heads to be used from heads 60 ₃, 60 ₄, and 60 ₁ to heads 60 ₄, 60₁, and 60 ₂ when wafer stage WST1 passes through a switching occurrenceposition P₆ on the +Y side of the twelfth shot area S₁₂ at a constantspeed. Here, main controller 20 resets measurement value C₂ of head 60 ₂which is to be newly used after the linkage process previouslydescribed, or in other words, after the switching, using coordinateoffset O which is obtained by the linkage computing, so that thecontinuity of the measurement results of the position of wafer stageWST1 before and after the switching is secured.

After the switching, main controller 20 moves wafer stage WST1 in aconstant velocity along a straight line path (scanning exposure path)indicated by a solid line in FIG. 16A, according to the measurementresults of heads 60 ₄, 60 ₁, and 60 ₂ (encoders 70 ₄, 70 ₁, and 70 ₂).This allows exposure area IA (exposure center P) to move at a constantvelocity from the +Y edge to the −Y edge of shot area S₁₂, and scanningexposure of shot area S₁₂ is performed.

However, because the distance (distance of straight line section Q₆) inwhich wafer stage WST1 is driven at a constant speed is short in thelinkage computing during settlement time T_(b), a coordinate offset Owhich is sufficiently stable may not be obtained.

In order to prevent such a situation from occurring, as a first methodfor securing enough time for linkage computing (to obtain a sufficientlystable coordinate offset O), performing the linkage computing previouslydescribed while wafer stage WST1 is accelerated can be considered, or inother words, performing the linkage computing during the step movementof exposure center P toward shot area S_(it) along a U-shaped path inFIG. 16A, concurrently with driving wafer stage WST1 for a long curvesection Q₆′ which is passed during acceleration time Ta (or adeceleration overscan time T_(e) and acceleration time T_(a)). However,at this point, because wafer stage WST1 is accelerated, an error mayoccur on stage position measurement by encoder system 70.

In other words, as shown in FIG. 17A, with encoder system 70 in theembodiment, a measurement beam is irradiated from head 60 ₁ in parallelto the Z-axis, on scale plate 21 (22) facing head 60 ₁ installed inwafer stage WST1. However, for example, when an acceleration in adirection (the −X direction) shown by an arrow in FIG. 17B is applied towafer stage WST1, the setting position of encoder head 60 ₁ shiftsrelatively to the +X direction with respect to wafer stage WST1, and thesetting attitude is tilted to the θy direction. This makes themeasurement beam tilt, which is irradiated on a point of scale plate 21(22) shifted from the designed irradiation point, which in turn causes ameasurement error.

Therefore, taking into consideration that there may be cases whenlinkage computing is performed during the acceleration time, a relationbetween the acceleration of wafer stage WST1 (WST2) and the measurementerror of encoder system 70 (71) can be measured beforehand, and duringoperation of the exposure apparatus, the measurement results of encodersystem 70 (71) can be corrected using the actual measurement data. Or, ameasuring instrument which measures the position and tilt of heads 60 ₁to 60 ₄ can be provided in wafer stage WST1 (WST2), and the measurementvalues of heads 60 ₁ to 60 ₄ can be corrected, based on measurementresults of the measuring instrument.

As a second method for securing enough time for linkage computing, asshown in FIG. 16B, a redundant section Q₆″ can be provided in thestepping path so as to extend the section where wafer stage WST1 movesat a constant speed (in other words, section Q₆ in FIG. 16A), and thelinkage computing can be performed while wafer stage WST1 is driven at aconstant speed in the section.

As a third method for securing enough time for linkage computing, tocondition (B≧b_(i)+L+20 for the configuration and placement of encoderheads 60 ₁ to 60 ₄ and scale plate 21 previously described, a conditionB≧b_(i)+2La+2t can be considered to be added (in other words, change tocondition B≧b_(i)+Max (L, 2La)+2t), further taking into considerationdistance La in the Y-axis direction in the U-shaped stepping section.

FIG. 16C shows an enlarged view of the inside of circle C4 in FIG. 15.However, in FIG. 16C, according to condition B≧b_(i)+Max (L, 2La)+2tdescribed above, area B₀ expands in the Y-axis direction. In the case ofFIG. 16C, because the U-shaped stepping section is completely includedin area B_(O), after shot area S₁₉ has been exposed, the heads need tobe switched (the tenth switching in FIG. 15) only when the wafer stepsin the Y direction toward shot area S₂₀, and the third to ninthswitching and the eleventh to eighteenth switching no longer arenecessary.

Incidentally, condition B≧b_(i)+Max (L, 2La)+2t can be applied not onlyto a shot arrangement where an even number of shot areas are arranged inthe Y-axis direction like in wafer W₂, and can also be applied to anarbitrary shot arrangement.

Next, after exposure center P performs exposure processing on the29^(th) shot area S₂₉ to the 31^(st) shot area S₃₁ and has moved fromarea B₄ to area B₀, switching of the head (a nineteenth switching)occurs when exposure processing of the 32^(nd) shot area S₃₂ within areaB₀ is performed and exposure center P is stepped to the 33^(rd) shotarea S₃₃ within area B₃. In this case, the heads to be used are switchedfrom heads 60 ₃, 60 ₄, and 60 ₁ to heads 60 ₂, 60 ₃, and 60 ₄. Thedetails are similar to the first switching previously described.

Similarly, after exposure center P performs exposure processing on the36^(th) shot area S₃₆ and has moved from area B₃ to area B₀, switchingof the head (a twentieth switching) occurs when exposure processing ofthe 37^(th) shot area S₃₇ within area B₀ is performed and exposurecenter P is stepped to the 38^(th) shot area S₃₈ within area B₄. In thiscase, the heads to be used are switched from heads 60 ₂, 60 ₃, and 60 ₄to heads 60 ₃, 60 ₄, and 60 ₁. The details in this case are also similarto the first switching previously described.

Due to the switching procedure and the linkage process described above,because switching of the heads do not occur during the scanning exposureof each shot area on the wafer in the exposure operation by thestep-and-scan method, sufficient overlay accuracy is maintained, and astable exposure processing of the wafer can be realized. Further, duringthe scanning exposure, main controller 20 performs the linkage computingwhile wafer stage WST1 (WST2) moves at a constant speed, and thenperforms the linkage process and exchange of the heads using the resultsimmediately after the scanning exposure. Or, main controller 20 performslinkage computing while wafer stage WST1 (WST2) moves at a constantspeed during the stepping movement, or performs linkage computing whilecorrecting the acceleration during the acceleration movement, and usingthe measurement results, performs the linkage process and switching ofthe heads just before the scanning exposure. This allows the continuityof the position coordinate of the wafer stage computed before and afterthe switching to be secured.

Next, the principle of position measurement in directions of threedegrees of freedom (Z, θx, θy) by encoder systems 70 and 71 will befurther described. Here, measurement results or measurement values ofencoder heads 60 ₁ to 60 ₄ or encoders 70 ₁ to 70 ₄ refer to measurementresults of encoder heads 60 ₁ to 60 ₄ or encoders 70 ₁ to 70 ₄ in theZ-axis direction.

In the embodiment, by employing a configuration and an arrangement ofencoder heads 60 ₁ to 60 ₄ and scale plate 21 as is previouslydescribed, at least three of the encoders head 60 ₁ to 60 ₄ face(corresponding sections 21 ₁ to 21 ₄ of) scale plate 21 according toarea A₀ to A₄ where wafer stage WST1 (WST2) is located within theexposure time movement area. Effective measurement values are sent tomain controller 20 from the heads (encoders) facing scale plate 21.

Main controller 20 computes the position (Z, θx, θy) of wafer stage WST1(WST2), based on measurement results of encoders 70 ₁ to 70 ₄. Here, themeasurement values (each expressed as D₁ to D₄, respectively, todistinguish the values from measurement values C₁ to C₄ in a measurementdirection which is not in the Z-axis direction as is previouslydescribed, namely, in a uniaxial direction in the XY plane) of encoders70 ₁ to 70 ₄ in the Z-axis direction depend upon the position (Z, θx,θy) of wafer stage WST1 (WST2) as in formulas (5) to (8) below.

D ₁ =−p tan θy+p tan θx+Z  (5)

D ₂ =p tan θy+p tan θx+Z  (6)

D ₃ =p tan θy−p tan θx+Z  (7)

D ₄ =−p tan θy−p tan θx+Z  (8)

However, p is the distance (refer to FIG. 5) of the head in the X-axisand the Y-axis directions from the center of wafer table WTB1 (WTB2).

Main controller 20 selects the formulas that the measurement values ofthe three heads (encoders) follow according to areas A₀ to A₄ wherewafer stage WST1 (WST2) is positioned from formula (5) to (8) describedabove, and by substituting and solving the measurement values of thethree heads (encoders) into the simultaneous equation built from thethree formulas which were selected, the position (Z, θx, θy) of waferstage WST1 (WST2) is computed. For example, when wafer stage WST1 (orWST2) is located in the first area A₁, main controller 20 forms asimultaneous equation from formulas (5), (6) and (8) that measurementvalues of heads 60 ₁, 60 ₂, and 60 ₄ (encoders 70 ₁, 70 ₂, and 70 ₄)follow, and solves the simultaneous equation by substituting themeasurement values into the left side of formulas (5), (6) and (8),respectively.

Incidentally, in the case wafer stage WST1 (WST2) is located in the 0tharea A₀, three heads from heads 60 ₁ to 60 ₄ (encoders 70 ₁ to 70 ₄) canbe randomly selected, and a simultaneous equation made from the formulasthat the measurement values of the selected three heads follow can beused.

Based on the computation results (Z, θx, θy) above and step information(focus mapping data) previously described, main controller 20 performs afocus leveling control on wafer stage WST1 (WST2) within the exposuretime movement area.

In the case wafer stage WST1 (or WST2) is located within measurementtime movement area, main controller 20 measures the positionalinformation in directions of three degrees of freedom (Z, θx, θy), usingencoder system 70 or 71. The measurement principle and the like, here,is the same as in the case when wafer stage WST1 is located within theexposure time movement area previously described, except for the pointwhere the exposure center is replaced with the detection center ofalignment system ALG, and (sections 21 ₁ to 21 ₄ of) scale plate 21 isreplaced with (sections 22 ₁ to 22 ₄ of) scale plate 22. Based on themeasurement results of encoder system 70 or 71, main controller 20performs a focus leveling control on wafer stage WST1 (WST2).Incidentally, in the measurement time movement area (measurementstation), focus leveling does not necessarily have to be performed. Inother words, a mark position and the step information (focus mappingdata) should be obtained in advance, and by deducting the Z tilt of thewafer stage at the time of obtaining the step information from the stepinformation, the step information of the reference surface of the waferstage, such as the step information with the upper surface serving asthe reference surface, should be obtained. And, at the time of exposure,focus leveling becomes possible based on the positional information indirections of three degrees of freedom (Z, θx, θy) of this stepinformation and (the reference surface of) the wafer surface.

Furthermore, main controller 20 switches and uses three heads thatinclude at least one different head out of heads 60 ₁ to 60 ₄ that facescale plates 21 and 22, according to the position of wafer stages WST1and WST2. In this case, when an encoder head is switched, the linkageprocess similar to the one previously described is performed to securethe continuity of the measurement results of the position of wafer stageWST1 (or WST2).

As discussed in detail above, in exposure apparatus 100 of theembodiment, encoder systems 70 and 71 are provided which measure thepositional information of wafer stages WST1 and WST2 in directions ofsix degrees of freedom (X, Y, Z, θx, θy, and θz) by irradiatingmeasurement beams from the four heads 60 ₁ to 60 ₄ installed in waferstages WST1 and WST2 on scale plate 21 that covers the movable range ofwafer stages WST1 and WST2 except for the area right below projectionoptical system PL (alignment system ALG). And, placement distances A andB of heads 60 ₁, to 60 ₄ are each set to be larger than width a_(i) andb_(i) of the opening of scale plates 21 and 22, respectively. Thisallows the positional information of wafer stages WST1 and WST2 to beobtained (measured), by switching and using the three heads facing scaleplates 21 and 22 out of the four heads 60 ₁ to 60 ₄ according to theposition of wafer stages WST1 and WST2.

Furthermore, with exposure apparatus 100 of the embodiment, placementdistances A and B of heads 60 ₁ to 60 ₄ are each set larger than the sumof width a_(i) and b_(i) of the opening of scale plates 21 and 22 andwidth W and L of the shot area. This allows the positional informationof wafer stages WST1 and WST2 to be obtained without the heads 60 ₁ to60 ₄ being switched, while wafer stages WST1 and WST2 which hold a waferfor exposure of the wafer is scanned (in constant velocity) and driven.Accordingly, the pattern can be formed on the wafer with good accuracy,and especially for exposure from the second layer onward, the overlayaccuracy can be maintained with high precision.

Further, in exposure apparatus 100 of the embodiment, by using themeasurement results of the positional information of wafer stages WST1and WST2 measured by the four heads 60 ₁ to 60 ₄, wafer stages WST1 andWST2 holding the wafer are scanned (in constant velocity) and driven toexpose the shot areas subject to exposure on the wafer, and after thedrive, three heads which make a set used for measuring the positionalinformation from the four heads 60 ₁ to 60 ₄ are switched to another set(including at least one different head), according to the position ofwafer stages WST1 and WST2. Or, by using the measurement results of thepositional information, wafer stages WST1 and WST2 are driven andstepped to a starting point of scanning (in constant velocity) for theshot areas subject to exposure, and after the stepping movement, beforewafer stages WST1 and WST2 are scanned (in constant velocity) and drivento expose the shot areas subject to exposure, the heads which make a setused for measuring the positional information from the four heads 60 ₁to 60 ₄ are switched to another set (including a different head). Thisallows the positional information of wafer stages WST1 and WST2 to beobtained without the heads 60 ₁ to 60 ₄ being switched, while waferstages WST1 and WST2 which hold a wafer for exposure of the wafer isscanned (in constant velocity) and driven. Accordingly, the pattern canbe formed on the wafer with good accuracy, and especially for exposurefrom the second layer onward, the overlay accuracy can be maintainedwith high precision.

Incidentally, in the embodiment above, at least one auxiliary head canbe provided in the vicinity of each of the heads on the four corners ofthe upper surface of the wafer table, and in the case a measurementabnormality occurs in the main heads, the measurement can be continuedby switching to the auxiliary head nearby.

Incidentally, in the embodiment above, while the case wheretwo-dimensional diffraction grating RG was formed on the lower surfaceof sections 21 ₁ to 21 ₄ of scale plate 21 and sections 22 ₁ to 22 ₄ ofscale plate 22 was described as an example, besides this, the embodimentdescribed above can also be applied in the case where a one-dimensionaldiffraction grating whose periodic direction is only in the measurementdirection (in a uniaxial direction within the XY plane) of thecorresponding encoder heads 60 ₁ to 60 ₄ is formed.

Further, in the embodiment above, as each of the heads 60 ₁ to 60 ₄(encoders 70 ₁ to 70 ₄), while the case has been described where atwo-dimensional encoder whose measurement direction is in a uniaxialdirection within the XY plane and in the Z-axis direction was employedas an example, besides this, a one-dimensional encoder whose measurementdirection is in a uniaxial direction within the XY plane and aone-dimensional encoder (or a surface position sensor and the like of anon-encoder method) whose measurement direction is in the Z-axisdirection can also be employed. Or, a two-dimensional encoder whosemeasurement direction is in two axial directions which are orthogonal toeach other in the XY plane can be employed. Furthermore, athree-dimensional encoder (3 DOF sensor) whose measurement direction isin the X-axis, the Y-axis, and the Z-axis direction can also beemployed.

Incidentally, in the embodiment described above, while the case has beendescribed where the exposure apparatus is a scanning stepper, thepresent invention is not limited to this, and the embodiment describedabove can also be applied to a static exposure apparatus such as astepper. Even in the case of a stepper, by measuring the position of astage on which the object subject to exposure is mounted using anencoder, position measurement error caused by air fluctuation cansubstantially be nulled, which is different from when measuring theposition of this stage by an interferometer, and it becomes possible toposition the stage with high precision based on the measurement valuesof the encoder, which in turn makes it possible to transfer a reticlepattern on the wafer with high precision. Further, the embodimentdescribed above can also be applied to a projection exposure apparatusby a step-and-stitch method that synthesizes a shot area and a shotarea. Moreover, the embodiment described above can also be applied to amulti-stage type exposure apparatus equipped with a plurality of waferstages, as is disclosed in, for example, U.S. Pat. No. 6,590,634, U.S.Pat. No. 5,969,441, U.S. Pat. No. 6,208,407 and the like. Further, theembodiment described above can also be applied to an exposure apparatuswhich is equipped with a measurement stage including a measurementmember (for example, a reference mark, and/or a sensor and the like)separate from the wafer stage, as disclosed in, for example, U.S. PatentApplication Publication No. 2007/0211235, and U.S. Patent ApplicationPublication No. 2007/0127006 and the like.

Further, the exposure apparatus in the embodiment above can be of aliquid immersion type, like the ones disclosed in, for example, PCTInternational Publication No. 99/49504, U.S. Patent ApplicationPublication No. 2005/0259234 and the like.

Further, the magnification of the projection optical system in theexposure apparatus of the embodiment above is not only a reductionsystem, but also may be either an equal magnifying system or amagnifying system, and projection optical system PL is not only adioptric system, but also may be either a catoptric system or acatadioptric system, and in addition, the projected image may be eitheran inverted image or an upright image.

In addition, the illumination light IL is not limited to ArF excimerlaser light (with a wavelength of 193 nm), but may be ultraviolet light,such as KrF excimer laser light (with a wavelength of 248 nm), or vacuumultraviolet light, such as F₂ laser light (with a wavelength of 157 nm).As disclosed in, for example, U.S. Pat. No. 7,023,610, a harmonic wave,which is obtained by amplifying a single-wavelength laser beam in theinfrared or visible range emitted by a DFB semiconductor laser or fiberlaser as vacuum ultraviolet light, with a fiber amplifier doped with,for example, erbium (or both erbium and ytterbium), and by convertingthe wavelength into ultraviolet light using a nonlinear optical crystal,can also be used.

Further, in the embodiment above, a transmissive type mask (reticle) isused, which is a transmissive substrate on which a predetermined lightshielding pattern (or a phase pattern or a light attenuation pattern) isformed. Instead of this reticle, however, as is disclosed in, forexample, U.S. Pat. No. 6,778,257 description, an electron mask (which isalso called a variable shaped mask, an active mask or an imagegenerator, and includes, for example, a DMD (Digital Micromirror Device)that is a type of a non-emission type image display device (spatiallight modulator) or the like) on which a light-transmitting pattern, areflection pattern, or an emission pattern is formed according toelectronic data of the pattern that is to be exposed can also be used.In the case of using such a variable shaped mask, because the stagewhere a wafer, a glass plate or the like is mounted is scanned withrespect to the variable shaped mask, an equivalent effect as theembodiment above can be obtained by measuring the position of the stageusing an encoder.

Further, as is disclosed in, for example, PCT International PublicationNo. 2001/035168, the embodiment above can also be applied to an exposureapparatus (lithography system) that forms line-and-space patterns on awafer W by forming interference fringes on wafer W.

Moreover, as disclosed in, for example, U.S. Pat. No. 6,611,316, theembodiment above can also be applied to an exposure apparatus thatsynthesizes two reticle patterns via a projection optical system andalmost simultaneously performs double exposure of one shot area by onescanning exposure.

Incidentally, an object on which a pattern is to be formed (an objectsubject to exposure to which an energy beam is irradiated) in theembodiment above is not limited to a wafer, but may be other objectssuch as a glass plate, a ceramic substrate, a film member, or a maskblank.

The application of the exposure apparatus is not limited to an exposureapparatus for fabricating semiconductor devices, but can be widelyadapted to, for example, an exposure apparatus for fabricating liquidcrystal devices, wherein a liquid crystal display device pattern istransferred to a rectangular glass plate, as well as to exposureapparatuses for fabricating organic electroluminescent displays, thinfilm magnetic heads, image capturing devices (e.g., CCDs),micromachines, and DNA chips. Further, the embodiment described abovecan be applied not only to an exposure apparatus for producingmicrodevices such as semiconductor devices, but can also be applied toan exposure apparatus that transfers a circuit pattern onto a glassplate or silicon wafer to produce a mask or reticle used in a lightexposure apparatus, an EUV exposure apparatus, an X-ray exposureapparatus, an electron-beam exposure apparatus, and the like.

Incidentally, the disclosures of all publications, the Published PCTInternational Publications, the U.S. patent applications and the U.S.patents that are cited in the description so far related to exposureapparatuses and the like are each incorporated herein by reference.

Incidentally, electronic devices such as a semiconductor aremanufactured through the steps of; a step where the function/performancedesign of the device is performed, a step where a reticle based on thedesign step is manufactured, a step where a wafer is manufactured fromsilicon materials, a lithography step where the pattern formed on a maskis transferred onto an object such as the wafer by the exposureapparatus in the embodiment above, a development step where the waferthat has been exposed is developed, an etching step where an exposedmember of an area other than the area where the resist remains isremoved by etching, a resist removing step where the resist that is nolonger necessary when etching has been completed is removed, a deviceassembly step (including a dicing process, a bonding process, thepackage process), inspection steps and the like. In this case, becausethe exposure apparatus and the exposure method in the embodiment aboveis used in the lithography step, devices having high integration can beproduced with good yield.

Further, the exposure apparatus (pattern formation apparatus) of theembodiment above is manufactured by assembling various subsystems, whichinclude the respective constituents that are recited in the claims ofthe present application, so as to keep predetermined mechanicalaccuracy, electrical accuracy and optical accuracy. In order to securethese various kinds of accuracy, before and after the assembly,adjustment to achieve the optical accuracy for various optical systems,adjustment to achieve the mechanical accuracy for various mechanicalsystems, and adjustment to achieve the electrical accuracy for variouselectric systems are performed. A process of assembling varioussubsystems into the exposure apparatus includes mechanical connection,wiring connection of electric circuits, piping connection of pressurecircuits, and the like among various types of subsystems. Needless tosay, an assembly process of individual subsystem is performed before theprocess of assembling the various subsystems into the exposureapparatus. When the process of assembling the various subsystems intothe exposure apparatus is completed, a total adjustment is performed andvarious kinds of accuracy as the entire exposure apparatus are secured.Incidentally, the making of the exposure apparatus is preferablyperformed in a clean room where the temperature, the degree ofcleanliness and the like are controlled.

While the above-described embodiment of the present invention is thepresently preferred embodiment thereof, those skilled in the art oflithography systems will readily recognize that numerous additions,modifications, and substitutions may be made to the above-describedembodiment without departing from the spirit and scope thereof. It isintended that all such modifications, additions, and substitutions fallwithin the scope of the present invention, which is best defined by theclaims appended below.

What is claimed is:
 1. An exposure apparatus that exposes a substrate with an illumination light via a projection optical system, the apparatus comprising: a first stage disposed above the projection optical system, that holds a mask illuminated with the illumination light; a first drive system having a motor to drive the first stage; a first encoder system that measures positional information of the first stage; a base disposed below the projection optical system; a second stage disposed on the base and having a holder to hold the substrate; a second drive system that has a planar motor of a magnetic levitation type and drives the second stage, the planar motor supporting the second stage by levitation on the base; a second encoder system that has four heads provided at the second stage and measures positional information of the second stage in directions of six degrees of freedom, the four heads each irradiating a measurement beam to a scale member from below, the scale member having four sections and an opening that is substantially surrounded by the four sections, each of the four sections having a reflection-type grating formed, and the directions of six degrees of freedom including a first direction and a second direction orthogonal to each other in a predetermined plane that is perpendicular to an optical axis of the projection optical system; and a controller that controls the first drive system and the second drive system based on measurement information of the first encoder system and measurement information of the second encoder system, respectively, and also controls the first and the second drive systems so that the mask and the substrate are each moved relative to the illumination light in scanning exposure of the substrate, wherein the scale member is provided on a lower end side of the projection optical system so that the projection optical system is located in the opening, the controller controls the second drive system so that the second stage is moved in a movement area that includes a first area and four second areas, in the first area the four heads respectively facing the four sections, and each of the four second areas having a part different from the first area, controls the second drive system so that the second stage is moved from one second area of the four second areas to another second area, different from the one second area, of the four second areas, via the first area, in the one second area, three heads of the four heads respectively facing three sections of the four sections, and in the another second area, three heads consisting of another head and two heads respectively facing three sections consisting of another section and two sections, the another head being of the four heads and being different from the three heads used in the one second area, the two heads being of the three heads used in the one second area, the another section being of the four sections and being different from the three sections used in the one second area, and the two sections being of the three sections used in the one second area, and in order to move the second stage in the another second area, switches one head, different from the two heads, of the three heads used in the one second area to the another head so that drive control of the second stage by three heads, including the another head and the two heads, that are used in the another second area is performed, instead of drive control of the second stage by the three heads used in the one second area, and the switching is performed while the second stage is in the first area.
 2. The exposure apparatus according to claim 1, wherein in a part of the another second area, the one head does not face the another section and one section that is different from the two sections, of the four sections, and in a part of the one second area, the another head does not face the another section.
 3. The exposure apparatus according to claim 1, wherein while the second stage is in the first area, the drive control of the second stage by the three heads used in the another second area is performed, instead of the drive control of the second stage by the three heads used in the one second area.
 4. The exposure apparatus according to claim 1, wherein the controller moves the second stage in the another second area, using correction information for compensating for a measurement error of the second encoder system, the measurement error occurring due to performing the drive control of the second stage by the three heads used in the another second area, instead of the drive control of the second stage by the three heads used in the one second area.
 5. The exposure apparatus according to claim 4, wherein the correction information is acquired while the second stage is in the first area.
 6. The exposure apparatus according to claim 5, wherein the measurement error occurs due to one of the heads and one of the sections used in the measurement being different between the one second area and the another second area.
 7. The exposure apparatus according to claim 5, wherein the correction information includes an offset for compensating for a difference between positional information of the second stage in the first area that is obtained from the three heads used in the one second area and the positional information of the second stage in the first area that is obtained from the three heads used in the another second area.
 8. The exposure apparatus according to claim 1, wherein each of the four heads is capable of measuring positional information of the second stage in two directions that are a direction parallel to the predetermined plane and a direction orthogonal to the predetermined plane.
 9. The exposure apparatus according to claim 1, further comprising: a metrology frame that supports the projection optical system, wherein the scale member is supported in a suspended manner from the metrology frame so that the reflection-type grating of the scale member is substantially parallel to the predetermined plane and the scale member is disposed on a lower end side of the projection optical system.
 10. The exposure apparatus according to claim 9, wherein each of the four sections has the reflection-type grating formed, and is substantially L-shaped.
 11. The exposure apparatus according to claim 9, wherein each of the four sections has a non-effective area on its outer periphery.
 12. The exposure apparatus according to claim 9, wherein the four heads are provided at the second stage so that a distance between each of the heads and the other heads is larger than a width of the opening in at least one of the first and the second directions.
 13. The exposure apparatus according to claim 12, wherein the four heads are provided at the second stage so that a distance between two heads of the four heads is larger than a width of the opening in the first direction and also a distance between two heads of the four heads is larger than a width of the opening in the second direction.
 14. The exposure apparatus according to claim 9, further comprising: a detection system provided at the metrology frame, away from the projection optical system, that detects positional information of the substrate; and another scale member different from the scale member, the another scale member having four sections which are different from the four sections of the scale member and each of which has a reflection-type grating formed, wherein the another scale member is supported in a suspended manner from the metrology frame so that the detection system is located in an opening of the another scale member and the another scale member is disposed on a lower end side of the detection system, and during a detection operation of the substrate with the detection system, positional information of the second stage is measured with the second encoder system.
 15. The exposure apparatus according to claim 14, wherein the four heads are provided at the second stage so that a distance between each of the heads and the other heads is larger than a width of the opening of the another scale member in at least one of the first and the second directions.
 16. The exposure apparatus according to claim 1, wherein the second encoder system has at least one head that is different from the four heads and is disposed close to each of the four heads.
 17. The exposure apparatus according to claim 1, wherein the switching is performed at times other than a scanning exposure period in which the illumination light is irradiated on the substrate or other than a constant speed movement period of the second stage.
 18. The exposure apparatus according to claim 1, wherein the controller controls movement of the second stage while compensating for a measurement error of the second encoder system that occurs due to at least one of a production error of the scale member, acceleration of the second stage, and a position or a tilt of the head.
 19. The exposure apparatus according to claim 1, wherein the planar motor has a coil unit provided at one of the base and the second stage and a magnet unit provided at the other of the base and the second stage, and the base is used as a countermass of the second stage.
 20. The exposure apparatus according to claim 1, further comprising: another second stage disposed on the base and different from the second stage, wherein the second encoder system has four heads that are provided at the another second stage and are different from the four heads provided at the second stage, and the second encoder system measures positional information of the another second stage in the directions of six degrees of freedom with at least three of the four heads provided at the another second stage.
 21. An exposure method of exposing a substrate with an illumination light via a projection optical system, the method comprising: measuring positional information of a first stage with a first encoder system, the first stage being disposed above the projection optical system and holding a mask illuminated with the illumination light; moving a second stage with a planar motor of a magnetic levitation type that supports the second stage by levitation on a base disposed below the projection optical system, the second stage having a holder to hold the substrate; measuring positional information of the second stage in directions of six degrees of freedom with a second encoder system that has four heads provided at the second stage, the four heads each irradiating a measurement beam to a scale member from below, the scale member having four sections and an opening that is substantially surrounded by the four sections, each of the four sections having a reflection-type grating formed, and the directions of six degrees of freedom including a first direction and a second direction orthogonal to each other in a predetermined plane that is perpendicular to an optical axis of the projection optical system; and controlling movement of the first stage and movement of the second stage based on measurement information of the first encoder system and measurement information of the second encoder system, respectively, wherein scanning exposure of the substrate in which the mask and the substrate are each moved relative to the illumination light is performed, the scale member is provided on a lower end side of the projection optical system so that the projection optical system is located in the opening, the second stage is moved in a movement area that includes a first area and four second areas, in the first area the four heads respectively facing the four sections, and each of the four second areas having a part different from the first area, the second stage is moved from one second area of the four second areas to another second area, different from the one second area, of the four second areas, via the first area, in the one second area, three heads of the four heads respectively facing three sections of the four sections, and in the another second area, three heads consisting of another head and two heads respectively facing three sections consisting of another section and two sections, the another head being of the four heads and being different from the three heads used in the one second area, the two heads being of the three heads used in the one second area, the another section being of the four sections and being different from the three sections used in the one second area, and the two sections being of the three sections used in the one second area, in order to move the second stage in the another second area, one head, different from the two heads, of the three heads used in the one second area is switched to the another head so that drive control of the second stage by three heads, including the another head and the two heads, that are used in the another second area is performed, instead of drive control of the second stage by the three heads used in the one second area, in the another second area, the one head does not face one section that is different from the two sections of the three sections used in the one second area, and in the one second area, the another head does not face the another section, and the switching is performed while the second stage is in the first area.
 22. The exposure method according to claim 21, wherein in a part of the another second area, the one head does not face the another section and one section that is different from the two sections, of the four sections, and in a part of the one second area, the another head does not face the another section.
 23. The exposure method according to claim 21, wherein while the second stage is in the first area, the drive control of the second stage by the three heads used in the another second area is performed, instead of the drive control of the second stage by the three heads used in the one second area.
 24. The exposure method according to claim 21, wherein in order to move the second stage in the another second area, correction information for compensating for a measurement error of the second encoder system is used, the measurement error occurring due to performing the drive control of the second stage by the three heads used in the another second area, instead of the drive control of the second stage by the three heads used in the one second area.
 25. The exposure method according to claim 24, wherein the correction information is acquired while the second stage is in the first area.
 26. The exposure method according to claim 25, wherein the measurement error occurs due to one of the heads and one of the sections used in the measurement being different between the one second area and the another second area.
 27. The exposure method according to claim 25, wherein the correction information includes an offset for compensating for a difference between positional information of the second stage in the first area that is obtained from the three heads used in the one second area and the positional information of the second stage in the first area that is obtained from the three heads used in the another second area.
 28. The exposure method according to claim 21, wherein each of the four heads is capable of measuring positional information of the second stage in two directions that are a direction parallel to the predetermined plane and a direction orthogonal to the predetermined plane.
 29. The exposure method according to claim 21, wherein the scale member is supported in a suspended manner from a metrology frame that supports the projection optical system so that the scale member is disposed on a lower end side of the projection optical system and the reflection-type grating of the scale member is substantially parallel to the predetermined plane.
 30. The exposure method according to claim 29, wherein each of the four sections has the reflection-type grating formed, and is substantially L-shaped.
 31. The exposure method according to claim 29, wherein the four heads are provided at the second stage so that a distance between two heads of the four heads is larger than a width of the opening in the first direction, and also a distance between two heads of the four heads is larger than a width of the opening in the second direction.
 32. The exposure method according to claim 29, wherein positional information of the substrate is detected with a detection system that is provided at the metrology frame, away from the projection optical system, another scale member is supported in a suspended manner from the metrology frame so that the detection system is located in an opening of the another scale member and another scale member is disposed on a lower end side of the detection system, the another scale member being different from the scale member and having four sections which are different from the four sections of the scale member and each of which has a reflection-type grating formed, and during a detection operation of the substrate with the detection system, positional information of the second stage is measured with the second encoder system.
 33. The exposure method according to claim 32, wherein the four heads are provided at the second stage so that a distance between each of the heads and the other heads is larger than a width of the opening of the another scale member in at least one of the first and the second directions.
 34. The exposure method according to claim 21, wherein positional information of the second stage is measured with at least one head that is different from the four heads and is disposed close to each of the four heads.
 35. The exposure method according to claim 21, wherein the switching is performed at times other than a scanning exposure period in which the illumination light is irradiated on the substrate or other than a constant speed movement period of the second stage.
 36. The exposure method according to claim 21, wherein the second stage is moved while a measurement error of the second encoder system is compensated for, the measurement error occurring due to at least one of a production error of the scale member, acceleration of the second stage, and a position or a tilt of the head.
 37. A device manufacturing method, comprising: exposing a substrate using the exposure method according to claim 21; and developing the substrate that has been exposed.
 38. A device manufacturing method, comprising: exposing a substrate using the exposure apparatus according to claim 1; and developing the substrate that has been exposed.
 39. A making method of an exposure apparatus that exposes a substrate with an illumination light via a projection optical system, the method comprising: providing a first stage that is disposed above the projection optical system and holds a mask illuminated with the illumination light; providing a first drive system having a motor to drive the first stage; providing a first encoder system that measures positional information of the first stage; providing a base disposed below the projection optical system; providing a second stage disposed on the base and having a holder to hold the substrate; providing a second drive system that has a planar motor of a magnetic levitation type and drives the second stage, the planar motor supporting the second stage by levitation on the base; providing a second encoder system that has four heads provided at the second stage and measures positional information of the second stage in directions of six degrees of freedom, the four heads each irradiating a measurement beam to a scale member from below, the scale member having four sections and an opening that is substantially surrounded by the four sections, each of the four sections having a reflection-type grating formed, and the directions of six degrees of freedom including a first direction and a second direction orthogonal to each other in a predetermined plane that is perpendicular to an optical axis of the projection optical system; and providing a controller that controls the first drive system and the second drive system based on measurement information of the first encoder system and measurement information of the second encoder system, respectively, and also controls the first and the second drive systems so that the mask and the substrate are each moved relative to the illumination light in scanning exposure of the substrate, wherein the scale member is provided on a lower end side of the projection optical system so that the projection optical system is located in the opening, the controller controls the second drive system so that the second stage is moved in a movement area that includes a first area and four second areas, in the first area the four heads respectively facing the four sections, and each of the four second areas having a part different from the first area, controls the second drive system so that the second stage is moved from one second area of the four second areas to another second area, different from the one second area, of the four second areas, via the first area, in the one second area, three heads of the four heads respectively facing three sections of the four sections, and in the another second area, three heads consisting of another head and two heads respectively facing three sections consisting of another section and two sections, the another head being of the four heads and being different from the three heads used in the one second area, the two heads being of the three heads used in the one second area, the another section being of the four sections and being different from the three sections used in the one second area, and the two sections being of the three sections used in the one second area, and in order to move the second stage in the another second area, switches one head, different from the two heads, of the three heads used in the one second area to the another head so that drive control of the second stage by three heads, including the another head and the two heads, that are used in the another second area is performed, instead of drive control of the second stage by the three heads used in the one second area, and the switching is performed while the second stage is in the first area. 